Unfortunately, no, no such platform exists.

The closest site I’ve seen getting to this was https://github.com/ZorrillosDev/watchit-app but their website seems offline for some reason.

Except tox’s graphical clients aren’t maintained anymore

Put simply, a bot that interfaces with external services and replicates messages to/from a Matrix chat. The software is at matrix.org

Which bridge did you use, if I may ask?

Maybe try a Matrix bridge?

As of August 2023, the best way to avoid the problem of

untampered compiler

AFAIK Is using an MNT Reform With GNU Guix as its OS, I really liked this article “The Full-Source Bootstrap: Building from source all the way down”. This approach could, potentially, solve the problem of the untampered compiler. Damn, maybe it already does.

As for the MNT Reform, the only thing I’m not sure is open is the actual processor firmware, but the schematics for its usage are available and even the Wifi firmware is open, so there remains the problem of actually verifying the hardware you get is actually the hardware you ordered, but that is a bit more complicated I think.