For me the last straw was notarization. I am not going to beg for permission to release software for Apple's platform. Considering the dire state of the Mac software scene Apple should be the ones on their hands and knees begging developers, the arrogance is incredible.
Apps aren't required to be notarized and it trivial for any vaguely competent person to dismiss the one-time warnings about unsigned apps. So it's only a big deal if you choose to make it one.
To be perfectly honest, if you can't even jump through that absurdly minimal hoop, I wouldn't want your software running on my mother's computer anyway.
Every time I see a developer completely fail to understand what notarisation is and how it works then proceed to say that their faulty understanding was the last straw and that they'll stop developing for macOS, I can't say I feel anything but delight. If basic reading comprehension is beyond so many developers, I can't imagine wanting their code on my machine, even in a sandbox.
I used to write a lot of apps for Mac. Including free and open source software. Now I have to pay $$$ and jump through hoops just to keep on doing it. It is amazingly arrogant for them to expect me to pay for doing them a free service. You can have as much autoschadenfreude as you want.
University students and people from countries on the US trade sanctions list will (I predict) not be able to share binaries in a future macOS, for example. It also gives apple a way to ban certain categories of program at the behest of the legal apparatus they have to operate in.
You can turn it off now, but you can't tell me you will always be able to turn it off.
I will abandon macOS when it is financially convenient - I hope you are delighted.
