I use sftp: https://source.puri.sm/Librem5/community-wiki/-/wikis/Tips-&-Tricks#ssh-file-transfer-protocol-sftp
If you’ve set up ssh, then you can access the L5’s directories directly from the file browser in your computer(s) over the wifi network. You can move individual files, multiple files, directories, or multiple directories all at once.
Or I just use a USB drive with both USB-A and USB-C ends.
There is Warpinator. (Also Warp.)
If you need to transfer between Android and the L5, I like SimpleSSHD from F-Droid. After connection, you have ssh and sftp functionality. See this tutorial.