Personal data?

I have it on my local network, not on the Internet.

Between phone and a computer KDE Connect is fantastic to move things back and forth.

And for any file on another PC, I just SFTP it. That's a centralized transfer because one computer is a server and the others are clients, but it's all my hardware, not "the cloud"

I don't have a need for anything fancier.

Ah, and if I have to send a file to someone outside, then I just upload it to one of my web servers and send the link.

This is for important stuff, for random things I use email, or whatever app they are using.