SimpleX isn't a fun or customisable messenger, so most people will not use it until it has the other features that Telegram or Signal have. Its funding sources/business structure are suspect, it could easily end up sold off and/or enshitified.
Also, SimpleX doesn't have easy or in some cases possible (as it isn't possible to access the file structure completely on some OSs) profile/message syncing on all platforms.
Finally, SimpleX isn't fully compatible with all devices and sticks them in an awful looking mode with no prioritised plans to fix this, Telegram and a few others don't have this problem.
Briar isn't on all platforms yet, so that's why there.
You're not there for fun lol, you're there to pirate stuff. Sure, using Signal to pirate would be fine too but your anonymity depends on how long they honor their word of "no logs". Use a desktop version/ run a VM if you're on MacOS or something.
Everybody hates me when I say it but Apple users should really reconsider their choices if they are at all interested in privacy. Go get a cheap Android device, hope it has a kernel beyond 5.10 and KernelSU it.
Anyway, what about the other issues I mentioned with SimpleX such as funding/business structure and no easy syncing?
You are assuming a lot about me, which is fair since I didn't give much to work with, but not accurate. Though, Android tablets are not all that great in my experience with them.