Using Ubuntu 20.04 with and Gnome 3.36.3, here is a bit more info about fstrim:-

edited@edited:~$ sudo systemctl status fstrim.timer
[sudo] password for edited: 
● fstrim.timer - Discard unused blocks once a week
     Loaded: loaded (/lib/systemd/system/fstrim.timer; enabled; vendor preset: >
     Active: active (waiting) since Fri 2020-11-20 09:21:54 GMT; 29min ago
    Trigger: Mon 2020-11-23 00:00:00 GMT; 2 days left
   Triggers: ● fstrim.service
       Docs: man:fstrim

Nov 20 09:21:54 edited systemd[1]: Started Discard unused blocks once a week.
lines 1-8/8 (END)
It looks like systemd is in the mix. I did not activate the trim service, I assume/guess it was activated during the install of Ubuntu 20.04 LTS