adbfs-rootless VS adb-sync

If you turn on ADB debugging in Chrome OS Settings > Advanced > Developers > Linux Development Environment > Develop Android Apps, you can install https://github.com/spion/adbfs-rootless on penguin and mount the entire Android File System wherever you want in Penguin

Another option would be to use adbfs to access the phone's filesystem

Back in 2018 there was this post about using rsync which generated a lot of discussion. The top comment recommended using adb-sync, and otherwise transferring with another network sync tool such as SyncThing or Resilio Sync had a lot of support.

I would recommend you put https://github.com/google/adb-sync in your ~/bin

If you want to backup your user storage to a PC the simplest option is to use ADB. Then there's also osm0sis' ADBsync sdcard backup based on adbsync.exe (https://forum.xda-developers.com/t/tools-zips-scripts-osm0sis-odds-and-ends-multiple-devices-platforms.2239421/) which works very nicely. And Google's own adb-sync (https://github.com/google/adb-sync)

adb-sync for file transfers. It's rsync over the adb protocol and functions much better than any of the MTP solutions.

nothing will be as quick as adb push (or use adb-sync - like a rsync from https://github.com/google/adb-sync ). That way you can sync a desktop folder to Android on a regular basis.

Not a solution to your problem, but I've found that adb-sync works really well for file transfer. I usually use it for backing up my phone storage, every month.

MTP is a sick, obnoxious joke perpetrated by an organization dedicated to proving "don't be evil" a lie. It is broken bullshit. You're better off giving up on it entirely and working entirely through ADB and the command-line. May I recommend the excellent adb-sync as a file synchronization and transfer tool that actually works.