Can I reenlist now that I’ve been in the Army for 30 months and my ETS is in December 2022?

Yes, you can, but your RCP is five years, meaning you can't reenlist longer than two years. You can't reenlist for much of anything for two years.

I don't know what you did to end up not getting promoted at your two year mark, but I would suggest asking your Career Counselor for a W extension, then once you're promoted reenlisting for what you want. You'll be back in your reenlistment window on October 1st.

Although, I will point out that your date of rank for SPC should be Aug 2021, unless you were flagged at that point, then it should be whenever your flag was removed. Go see your Career Counselor, they should be able to help you out. If not, message me and I will help you out

You're in your window now. I'm surprised you haven't been contacted by your designated Retention NCO/Career Counselor. I'm also surprised you don't know who that is. You've been a PFC for 1.5 years and in the Army for 2.5 years? Why are you not a SPC?

You are in your reenlistment window, but you have also been in long enough to be advanced to E4 but have not done so yet.
Are you currently flagged or barred from reenlistment?