Answer developed with Ubuntu 20.04 (see
lsb_release) and kernel version 5.4.0-137-generic (see
Mounting. Ubuntu recognized and mounted immediately an untouched 1.44MB 3.5" floppy disk inserted into an external USB floppy drive. In my case, the disk got auto-mounted to a
/dev/sdc device, rather than a
/dev/fd* one as you may find around.
gparted recognized a FAT16 filesystem in it. As you may know, floppy disks were sold already formatted.
ufiformat. I found the tool
ufiformat useful to learn more about the disk. This tool has been in the package kit since Bionic: see https://packages.ubuntu.com/search?keywords=ufiformat&searchon=names&suite=all§ion=all. It is aimed at formatting the disks, but the flag
-i shows device information only: see the manual pages at https://manpages.ubuntu.com/manpages/focal/man8/ufiformat.8.html. See this other post for getting insights from the 'generic drives'
\dev\sg: https://community.clearlinux.org/t/solved-how-to-handle-usb-floppy-drive-formatting-mounting-etc/905/6 This will help you see if you deal with a corrupted medium. Also, the information gave me confidence about the correct device file of the floppy disk.
Folklore. There's been some talk about floppy support being orphaned in the Linux kernel and the death of the floppy disk. See Torvalds' own commit message https://github.com/torvalds/linux/commit/47d6a7607443ea43dbc4d0f371bf773540a8f8f4 of 2019 concerning the kernel version 5.3. Something remedial or less ominous must have happened in the meantime, since I could read a healthy disk seamlessly with a kernel 5.4.
Basically, the only troubles I experienced are with floppy disks used and corrupted, not with the operating system and the distribution. I hope this is the case with Ubuntu 22 and onwards too.