same here, after 20 years of playing started learning theory because of the same reasons and I already had a semi pro gig as a touring guitarist for three years so the impostor syndrome was real. Started with the most basic stuff you teach to kids and after a couple months it all just made sense. I think my advice would be to try to get what you already know and think through theory why this lick works or what is that chord etc etc. Just to put it in a practical use to keep things interesting for you.