This one worked like a charm, thanks!

Doesn’t even connect to my smb, for reasons beyond my knowledge.

Tried it, but can’t seem to upload files to it via the Google Files app.

Material Files did what I wanted, but I ended up only uploading with 10KByte/s via this app (5ghz WiFi or 2.4Ghz, same speed). No clue what went wrong, but that’s quite unusable for me.