Planning on going from engineer officer 12A to engineer warrant officer 120A. What does this process look like?

Joey, my experiences are ancient, so take them with a five-pound bag of salt. I actually knew an MI guy who resigned his commission as a captain to accept a warrant. I don't recall if it was WO1 or CW2. Either way, from personal experience, being a warrant officer was a blast! I got to do all the hands-on stuff AND got to be a leader. I was never going to be a battalion commander, but then, my commanders were never going to get to do what I was doing. I would suggest giving the warrant officer in charge of that branch a call and discussing options from his or her perspective. He or she will be the person that you'll likely deal with on that side of the house. Once you get answers there, that will give you more concrete information to approach your current boss.

The first step is submitting a 'Conditional Rank Resignation' memorandum* HRC for a conditional release from your Branch Chief.

After that you would apply to the Warrant Officer Selection Board and include that as part of your packet*.

You'll have to look through the applicable MILPER messages for the year you (try to) make the switch to determine what constructive credit will apply. This will determine what, if any, PME you'll need to complete and what grade you'll be appointed at.

If anyone is telling you that any of your previous education/training 'will' count in regards to your WOBC, have them cite the applicable regulation and/or policy letter. Unless the course has been formally reviewed, and and guidance has been issued regarding what, if any, portion of XXXXX is satisfied by YYYYY, then it will be a judgement call regarding which training objectives required by the Program of Instruction (POI) are met.

In other words, BOLC and WOBC have two different focuses. There is a lot of overlap but some significant differences. You'll have to show that your totality of education/experience as a 2LT covers all the requirements from the WOBC POI.
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* Conditional Rank Resignation (template) - https://recruiting.army.mil/Portals/15/updated%2011_%20AV_Conditional_Rank_Resignation_MFR_TEMPLATE.docx
* Warrant Officer Application Checklist - https://recruiting.army.mil/Portals/15/Applicant%20Checklist_1%20Feb%202023.pdf

I'm confused. Why would you wait 10 years, a point at which you should at least be promotable to Major, to switch to Warrant? If being commissioned isn't your thing, why wait to try to switch?

If it's about 2LT being a shit job, it's a shit job in almost every branch. It gets better. Two of the best jobs I had in the Army were at Captains rank, Company Commander and Assistant Brigade Engineer. Most Officers remember their first Company Command as a highpoint of their service.