For your personal use KDE Connetc might be best. But for "hey can you send me this" https://pairdrop.net/ is just magic. 0 setup and works on all devices with a browser.
One might want to also have a look at murena cloud. It's hosted in france, based on nextcloud and has the benifit of also including a mailing service. Additionally they have a custom andriod.
https://murena.com/workspace/
For your personal use KDE Connetc might be best. But for "hey can you send me this" https://pairdrop.net/ is just magic. 0 setup and works on all devices with a browser.