Firebase is a platform/service provided by Google, so it makes sense that the content goes thru Google's servers.
Also, E2EE in a closed-source app like WhatsApp, run by a nefarious corporation like Meta, was always a joke concept, a marketing ploy at best. People who are truly concerned about their privacy would never touch WhatsApp.
The only Keen I know of (and acknowledge) is the Commander:
Speaking of German privacy tools... Win10privacy is still being updated from the looks of it, so that could be an option too.
Nothing beats Linux if you're want control over your system. As for gaming though, you can check this website to see whether your games are compatible or not: https://www.protondb.com/
And if your games are compatible, then look no further than Bazzite - it's a gaming-optimised distro that just works out-of-the-box, no need to manually install any drivers and stuff (you can of course use it for non-gaming tasks too).
Unfortunately Group Policy isn't bullet proof, Microsoft has a history of sneaking in "features" like this as part of an update, but without any corresponding policy to disable it.
Syncthing, it was made exactly for situations like this. And unlike DropBox etc your data stays local.
Mercury is worth checking out - it's based on Librewolf but has additional privacy and performance patches.
And refactor the code a bit to be on the safe side - change the name of the project and remove any references to litigious companies. And use an anonymous handle + VPN/proxy chains so they can't sue you.
Honestly it boggles my mind that devs contribute to emulators like these using identifiable names and traceable IPs, when everyone knows how these greedy corporations operate. Did no one learn anything from the Sony vs Geohotz case, or all the subsequent takedown against emulators? Why do these devs keep falling into the same trap again and again?
It was big among the netsec/sysadmin crowd too, it was the first place you'd hear of 0-days in the wild, or whether a popular site/service was down.