To be fair, the Audacity UX designer made a massive video about the next UX redesign and how he tried to get rid of "modes" and the "Audacity says no" problem:
https://www.youtube.com/watch?v=QYM3TWf_G38
So this problem should get better in the future. Good UX (doesn't necessarily have to have a flashy UI, but just a good UX) in free software is often lacking or an afterthought.
Now he got rid of the modes by adding handles and border actions - so 1) wasted some space that could be used for information 2) required more precision from the users because now to do the action you must target a tiny handle/border area 3) same, but for other actions as now you have to avoid those extra areas to do other tasks.
While this might be fine for casual users as it's more visible, the proper way out is, of course,... MODES and better ones! Let the default be some more casual mode with your handles, but then let users who want more ergonomics use a keybind to allow moving the audio segment by pressing anywhere in that segment, not just in the tiny handle at the top. And then you could also add all those handles to visually indicate that now segments are movable or turn your pointer into a holding hand etc.
Same thing in the example - instead of creating a whole new separate app with a button you could have a "1-button magicbrake" mode in handbrake
What is there to see? You add a bar that takes space. That space can be taken up by something useful. Just like you have apps that hide app title bar and app menus so you can have more space for your precious content. This is especially useful for high-info-density apps like these audio/video/photo authoring ones. Note how tiny those handles are in the video, why do you think that is?
> tradeoff is an incredible degree of customisation
You don't have that tradeoff, neither of the 2 solutions are anywhere close to "incredible customization", so you can pick either without it.
> In terms of precision, they're working on accessibility issues
Working towards what magic solution?
> but I'm not sure how this change is any special than any other UI.
why does it have to be special? Just a bog standard degradation common to any UI (re)design, nothing special about it.
> the modes were horrid
Of course they were. Just like they were horrid in that MS Paint app the dev worked on before. But you can make any UI primitive horrid, even buttons, that's no reason to remove them, but to improve them!