Yes, it is still OK to use those services. The law is aimed at the messaging/social media businesses, not individuals, and is vague enough that they won't have to do anything around their E2EE until there is viable technology available to square the circle of allowing for the checking of illegal abuse content while not functionally destroying E2EE. So potentially never.
This is what I use. Not amazing, but given it's possible to use Messenger through it as well if needed, it's better than nothing.
I'd been on the waitlist for more than a year, but finally on. I downloaded the app a little while ago to keep tabs on my progress through the waitlist and they definitely have been speeding up the process of getting people onboarded to be fair.
SlimSocial is the only one that I've found that still works, though might require some messing with the settings to get Messenger working through it.
Matrix bridges are an option for those willing to put the effort in and self-host. I might get round to doing this at some point.
It's not open-source, but I've settled on Beeper for the time being as the simplest option to get all my messages in one place.
Was this title intentionally written in a way as to make people think he had died?