I don’t know what goes into bundling/building a software package for FreeBSD.
We use electron-builder for creating the packages for the other platforms (linux, macOS, windows) and it does not have an option to build for FreeBSD yet. So I think its the same as for flatpack, a custom script/repo that builds for freebsd. Is there a docker image of FreeBSD on github actions or some other reliable way to cross compile for it?
There is an issue at electron about FreeBSD that is still open Add FreeBSD support to electron · Issue #3797 · electron/electron · GitHub.
Either way I think someone would have to try to build it there and see what problems appear and if they are easily fixable.
For discussion on non-electron clients I recommend these two threads:
DeltaChat running on mobian (PineTab, PinePhone)
Are there any native linux desktop apps in the works?