Correct me if I'm wrong but:
A fresh installation of Garuda Linux, contains the BTRFS Maintenance package, and it's configuration file located in
/etc/default/btrfsmaintenance, but the settings contained within the config file have not been applied by running the
btrfsmaintenance-refresh.service unit file once. When run, the systemd timers will update to match the values setup in the config file.
The config file has DEFRAG and TRIM disabled by default (as they should be!) but the systemd timers will still be running them periodically even if the config file has them disabled, because the config file changes have not been applied by running the refresh unit file above.
Edit: fixed 'default' typo