Posting from Mastodon can be done by mentioning the community as if they are a user eg

@community@lemmy.instance

Alternatively there is !bestoflemmy@lemmy.world

You can replace the default windows UI with an alternative shell like Open Shell (here’s a list). Not sure how reliable this works.

most of us wouldn’t want to have sex with tentacles and cat ears

They do advertise direct export, but I’m not sure if that means encrypted json

Proton does this as well, you can use it completely offline without an account