I read a comment on Reddit [0] from a Nokia user that had a large file transfer using Solid Explorer killed twice because he left the phone unattended and the screen shut off. It worked when he kept the screen on.

Would you mind testing if background file transfers work as standard and with manual battery optimization whitelisting?

[0] https://www.reddit.com/r/Nokia/comments/afkuh4/dontkillmyapp...