As a 6700XT owner, I use 4k@60Hz (my screens can’t do better anyway). Does that mean I would need to use DisplayPort for better output in the future?

For reference, I have a 6700XT on a 4k videoprojector, and it’s fluid for 4k video and games (but it’s a gaming card). The drivers are excellent and the card is stable. Thus said, I read some web videos through mpv, which is more optimized. On Youtube 4k, it works as well. I’ve tried 8k downsized and it was bit laggy, so I don’t think a 6400 is enough for 8k video. I also had to buy a HDMI cable with more throughput! Videos aside, I think it’s okay for the display only (texts and images), but wait for another reviewer because the 6400 is less powerful, so I can’t confirm. However, if it works on Windows, it will work on Linux.

I use FreshRSS since a few years and it’s excellent!

For links, I use Pocket (you can use Wallabag, but I find the interface not efficient at all). For files, you can sync a folder with syncthing (but you only switch it on when you want a quick sync, otherwise keep it off for battery). If you just want to put some file on your phone, install FTP server (free) from F-droid and switch it on when you need it (there’s even an optional switch on quick actions). Use Filezilla or any file browser (if on Linux) to exchange your files. Remember to switch the server off once finished, because FTP is not a secure protocol.

Nextcloud was too slow and bloated for me. I used Seafile for years and it was fine, but at some point I went to some more simple setup : sftpgo to share folders (sftp, dav) and syncthing for the folders I want to sync between devices. You can also set ignore lists in syncthing to ignore large dirs. Keep it simple stupid 😅