I’m on OpenRC, so I can’t say anything about systemd, but I have several SSHFS mounts (non-auto) listed in my fstab:

sshfs#root@192.168.0.123:/random-folder/ /mnt/random-folder fuse noauto,uid=1000,gid=100,allow_other 0 0

Is that similar to what you’ve tried in your fstab? I’d assume replacing noauto with auto should just work, but then again, I haven’t tried it (and rebooting my system right now would be very inconvenient, sorry).

It also might require you to either use password-based login and specify the password or store the SSH keys in the .ssh directory of the user doing the mount (should be root with auto set).