So how to completely disable Tracker, so it no longer indexes any files, and stop having any Tracker process running in the background? You can mask the Tracker systemd services to completely disable it for your current user using this command:

systemctl --user mask tracker-store.service tracker-miner-fs.service tracker-miner-rss.service tracker-extract.service tracker-miner-apps.service tracker-writeback.service

After this, reset Tracker:

tracker reset --hard

And reboot.

If you reboot your system after masking the Tracker services, you should no longer see any Tracker processes running in the background. Or run tracker status and it should not work, saying that the unit is masked (this only happens if you used both the mask and the Tracker reset commands). You may also run tracker daemon to check the status of the Tracker daemons (Tracker Store and Tracker Miners) - they should all be listed as disabled / not running:

Tracker daemons disabled

You may get a warning that some of these services do not exist - ignore it. That's because for example on Ubuntu 19.04 there's no tracker-miner-rss.service by default, but there is one on Solus OS and Fedora, which in turn do not have tracker-miner-apps.service.

When masking a systemd service, its unit file is symlinked to /dev/null, making it impossible to load the service, even when some other service tries to load it. This is better than disabling the service, because when disabled, a service may still be started if another service that depends on it is started.

Want to undo this change and enable Tracker back? Use:

systemctl --user unmask tracker-store.service tracker-miner-fs.service tracker-miner-rss.service tracker-extract.service tracker-miner-apps.service tracker-writeback.service

And reboot your system after this.