In my case, as a developer of a programming language that can compile to all supported platforms from any platform the signing (and notarization) is simply incompatible with the process.

Not only is such signing all about control (the Epic case is a great example of misuse and a reminder that anyone can be blocked by Apple) it is also anti-competitive to other programming languages.

I treat each platform as open only when it allows running unsigned binaries in a reasonable way (or self-signed, though that already has some baggage of needing to maintain the key). When it doesn't I simply don't support such platform.

Some closed platforms (iOS and Android[1]) can be still supported pretty well using PWAs because the apps are fullscreen and self-contained unlike the desktop.

[1] depending on if Google will provide a reasonable way to run self-signed apps, but the trust that it will remain open in the future is already severely damaged