The Signal messenger and protocol.

It’s a shame that Signal has discontinued its support for normal SMS,

While this does suck for those of us who used it, it was the cause of a few issues:

1. It was confusing to less "technical" users.
2. Because of point 1, it introduced a security/privacy weakness to its userbase in that users could be tricked into thinking their communications were secure/private.
3. The feature was poorly maintained due to the small team behind Signal and the decision to improve their platform vs supporting something they had minimal control over.
4. Signal's SMS feature was causing real-life delivery issues with some new users as RCS started rolling out. A user's phone would register with RCS - and if they installed signal -which then takes over SMS messaging but couldn't (thanks to Google) support RCS - they would stop receiving RCS messages. This is a problem caused by Google to their benefit.

hadn’t implemented RCS,

Signal cannot implement RCS on Android without Google providing an API like they did with SMS. Apple doesn't even allow alternative SMS clients so this made no sense going forward - basically SMS/MMS/RCS is a dead-end for Signal.

is spending too much effort on “stickers”

What year is this? Signal stickers were released at the end of 2019 [0] and, in the nearly five years since, the work to maintain them is so small it may as well be zero. Check github - the work they release is public and you can see exactly what they've been working on.

and now keeps prodding you to donate money.

Its a free service, god forbid they ask users to contribute so they can continue to exist and provide said service to those who can't afford it? 🤷‍♀️

Then there’s the broken notification with iOS users who just don’t find out that you messaged them until they launch the app.

Valid criticism IF true. I don't have an iOS device so I can't say much here but I do message iOS users pretty frequently and haven't had any problem with response times - not sure if that's because they're always on their phone or because notifications work in most cases.

As a direct result my use of Signal has pretty much ceased.

While unfortunate for your privacy, if you were primarily using Signal for SMS, you weren't really using Signal to begin with.

[0] https://signal.org/blog/make-privacy-stick/