Do you believe it is ok for active service members to degrade the POTUS on RP?

Also, being in the military, you have regulated limitation on your First amendment rights. Day 1 information.

Absolutely not. There are regulations against it.
I can tell you first-hand that when Obama was in office they were dutifully handing out UCMJ to anybody caught on post with anti-obama bumper stickers, or caught trashing him on social media.
I'm not sure if that same enthusiasm is prevalent today... But the standard should be the same.

No while in the service your CIC is not to be a topic of political disruption to the mission.

As far as veterans go, I believe that they should be able to speak freely to the extent allowed by the constitution and the bill of rights. On active duty, especially while in uniform, the old saw "respect the rank if not the person"; for better or worse POTUS is Commander In Chief.

If you are on active duty or even in the reserves or national guard then you should not be posting any disparaging comments on the POTUS.
If you are having a discussion about something that he has done that is different

What: General guidance for military personnel (including Reservists and NG) is set forth in DoD Directive 1344.10 "Political Activities by Members of the Armed Forces" (19 FEB 2008), PAG 2016 "DoD Public Affairs Guidance Concerning Political Campaigns and elections." and DoD Instruction 1334.01 "Wearing of the Uniform" (see also NAVPER 156651 and MCO P1020.34G).
BLUF: DoD Policy: "Members on Active Duty should not engage in partisan political activity, and members on active duty should avoid inferences that their political activities imply or appear to imply official sponsorship, approval, or endorsement." DoDD 1344.10, para. 4
"'Partisan political activity' is activity supporting or relating to candidates representing, or issues specifically identified with national State political parties and associated or ancillary organizations or clubs." DoDD 1344.10 Enclosure 2 (Definitions)
Who is Covered: Generally, ADC and NG (on active duty). Rules relating to campaign and partisan political activities while in uniform apply to retirees (i.e., don't use campaign materials where you are shown in uniform, but you can identify yourself as Ret. or a veteran).
What You CAN Do: Register and vote, express your political opinion in a personal capacity (in your civilian capacity, this gets into the tricky area of social media where you have do include a disclaimer if you are identifiable as military and cannot insert link to a partisan website or page or suggest that others "like", "friend" or "follow" a partisan account), encourage others to participate in the political process (but not vote a particular way), signs a petition for legislative action (in your civilian capacity), write a letter to the editor (but not as part of an organized letter writing campaign, e.g., NRA, Sierra Club, and only with a disclaimer), donate money to a political organization, party or committee, display a regular bumper sticker on your vehicle (not a huge banner or covering your vehicle).
What you CANNOT Do: Participate in partisan political fundraising activities (the prohibition includes forwarding invitations to others), publish partisan political articles, letters, or endorsements that solicit votes, speak before a partisan political gathering, participate in any radio, television or other program or group discussion as an advocate for a partisan party, candidate or cause, engaging in fundraising activities for any political cause or candidate on a military installation, or display a partisan political sign, poster, or banner visible to the public in military installation housing. Also prohibited: "Any activity that may be reasonably viewed as directly or indirectly associating the Department of Defense or any component of these Departments with a partisan political activity or is otherwise contrary to the spirit and intention of this Directive shall be avoided." DoDD 1344.10, para. 4.1.5.
Criticism of Senior Govt. Officials by Commissioned Officers is covered by UCMJ Art. 88 - Contempt Towards Officials. This includes the following: POTUS, VP, SECDEF, SEC of a Military Department, Congress, SECTRANS, and a Governor or Legislature when present or on duty in that state, territory or possession).
And then, there are the list of prohibitions against what you can and cannot do in uniform....
The DoDD applies mostly to Active Duty, but also to NG in active duty status. Parts appear to apply to Reservists and retirees (especially rules pertaining to the wearing of the uniform in a political context). You'll notice that LG McMaster stopped wearing his uniform when he became National Security Advisor.
Hope this provides some guidance.

Active Duty, Reserve and National Guard component service members absolutely should not make disparaging remarks about the President. However Veterans regained freedom of speech once their contractual military service ended. That said military related forums are not the place for political rhetoric in my opinion.

If you work for Amazon and disparaged Jeff Besos you wouldn’t have a job if they found out. Likewise the CINC is your CEO if you are active duty. You do not disparage the CEO of the organization you work for.

To quote an Australian general “If that does not suit you, then get out!”

It is actually against the law for members of the military (active, reserve & national guard, retired personnel may fall under this category as well) to openly degrade the POTUS. As members of the service, we are often seen as official spokes(wo)men just because we were the uniform. This is why the military has a Public Affairs Office. That is their job. As a member of the military, you actually gave up some of your rights under the constitution to be in the military (yes, officers included). In essence, no, I do not believe that ANY service member should be allowed to degrade the POTUS no matter who it is and their political stance. We have heard this before, we are NOT an organization that is supposed to be used as a politically pawn. We are here to train for, fight, and win wars, period.

Back when I was on active duty, in 1992 we elected as our President an individual that I personally thought was a scumbag. But I refused to express that opinion in any place where my private thoughts might be mistaken for a public display of disparagement. No one knew what I was thinking, what I really thought of my CinC. And, to express myself in a public forum of any kind might cause people to denigrate the military. I wanted to avoid all appearance of impropriety. My opinion is that it went against the Codes of Conduct and the UCMJ (as I understood it). I am not happy with his name on any of my paperwork, but it is what it is. I know that I didn't say all the right words here, my TBI and previous strokes sometimes causes me to not be able to make myself clearly understood.

No, this is not the place to 'blow off steam' or tell the world that you think your boss is an ass. Civilians read this too. But that isn't the only reason. For the good of the military. Or, for the overall morale of the people you work next to, and maybe depend on with your life. Or, to not give aid, comfort, and encouragement to those you are fighting against. Each of these reasons and many others should be sufficient for you to maintain the discipline necessary to ensure that you come home safe from the day's battles; that self-discipline to keep your thoughts to yourself and your mouth shut and your ears open.
After you leave the military, then that is the time for you to freely express yourself if you wish. Or, if you believe you could do a better job, and you can get enough of your friends to back you up, then run for Public Office and fix the things you didn't like.