with-emacs.sh VS emacs.onboard

Well, this is impossible to test if you don't say on what version of Emacs you're experiencing this. You could test if it is your configuration by using the lovely with-emacs script to sandbox.

Check out https://github.com/alphapapa/with-emacs.sh

FWIW, I would generally recommend using with-emacs.sh rather than chemacs2, because it's much simpler to use: https://github.com/alphapapa/with-emacs.sh

Whenever you encounter weird behavior, you should try to reproduce it in a clean Emacs config. This script makes that easy: https://github.com/alphapapa/with-emacs.sh

Not to poach, but you might try this alternative: https://github.com/alphapapa/with-emacs.sh

Wow, finally! And just when I've gotten the bugs ironed out of with-emacs.sh and makem.sh related to Emacs 28's changes. Well, pre-29 versions will still be around for a long time, so with-emacs.sh will remain useful, but it will be nice to have support for this integrated into Emacs.

Sure, but you don't have to throw away your old, comfortable, known-good config to try a new one. Use with-emacs.sh to run as many Emacs configs as you like.

And about 20 minutes later (native comp with full AOT takes a while), I could just run emacs-28.0.60 (or with my script, with-emacs.sh -e emacs-28.0.60 -d ~/src/emacs/configs/ap.el).

I just restarted using Emacs Onboard as a template. It's claim to fame is that it does not load in additional packages. In this way like better-defaults, but much more coverage. I'm a long time helm user who is tempted by ivy, but why not try icomplete-mode, which is built in? I really enjoy (fido-vertical-mode 1).