discard=async by default for devices that support it
The issue:
If You have multiple different filesystems Ext4, XFS and Btrfs …, disabling systemD service fstrim is not a good idea for all filesystems on multiple SSDs on your same computer.
If You need to fstrim other filesystems e.g. EXT4 and disable fstrim for Btrfs only.
Currently fstrim has no option to ignore any selected filesystem e.g. Btrfs, but there is a trick to exclude Btrfs from fstrim.
How to exclude or ignore Btrfs from fstrim service
I like your suggestion. But you do not need to add the first line for fstab, because mountinfo is sufficient and more flexible than fstab, it can detect when connecting any other external SSD via USB.
Yes, I did not know that before. Thanks for the suggestion. But the default config of fstrim.services uses mountinfo which collects all mount-points.
Update
Today, fstrim added a new option -t,--types to filter out by filesystems
I literally used the same command as the default service uses, just changed the files it uses, eg. double-collon separated and in same order
You are free to comment-out the first line ofcourse, which would result in only the mountinfo tobe used (Commenting is done using a # at line start)