I transferred fotos etc from Android 11 (Samsung S10e) to Ubuntu via USB; then, after completion, tried to unmount (I think) which then stalled (if I remember correctly) then pulled the plug and since then I can't properly mount/connect via USB again as before. - Of the USB connection options presented to me by Android, I can now only connect via "Transferring images" (also known perhaps as "PTP via USB turned on") instead of "Transferring files" (which worked before).
How to fix / reset the connection so that also the other connection mode ("Transferring files") will work again as before?
- I already rebooted both the phone and the laptop: no change.
/var/crashcontains _usr_libexec_gvfsd-mtp.1000.crash
I have problems too with mounting Android 11 (Motorola G20) on Ubuntu 20.04 LTS. It only works if I first select on the phone: USB Virtual Drive, which mounts an almost empty CD drive, then select on the phone: MTP, which then succeeds and shows the files from the phone.
Maybe this workaround works also for you.
While this may be a good solution (which I didn't yet try) a perhaps simpler and reliable solution for me was / is to use a standard USB flash drive (and, if needed, a USB-C/A adapter) instead of directly conneting to a PC / Ubuntu; this way, the drive is handled by Android directly and no need to get MTP to work...
Further links (including (Samsung-?)related bugs):