the employers behaviour here is offensive to any persons sensibilities and I think everyone reading this would be of the same mind to moving on as soon as possible. The way to do this is of course start talking with other employers, there is no reason why you couldn't rustle up some more suitable opportunities whilst you continue in post with this employer. Go only when you have found the right opportunity
IMO burnout is hard to identify in the moment, but looking back, its clear to see :). Keep your job for now, start the job hunt, and good luck.
Sorbet is something I've been interested in using for a couple years and finally got a round to actually trying it out. I tried to use Sorbet with ruby 3.1.1 but unfortunately it didn't "just work" which I think is crucial for mass adoption. I want to give the benefit of the doubt and say its my local env that causing issues with Sorbet but in a fresh `rails new test_app --api` project, I'd expect `srb init` to work without errors... maybe I need to give it another go, curious on your thoughts above tho! :)