[sneak]

Signal does not aggressively block non-official clients. I constantly use a modified version of Signal Desktop containing a small set of my own patches, and it always works fine. Also, while autoupdate is on by default for the Signal client (and it includes a time bomb expiration to attempt to "force" you to upgrade regularly (removing this is one of my patches)), you are free to turn it off and remove their ability to modify the code on your own system.

[p-e-w]

This doesn’t work on iOS, where you can’t selectively disable automatic updates for a single app.

[sneak]

I have all iOS automatic app updates disabled.