Not going to watch a video. I am gathering from comments on the youtube video that he is taking about telemetry data. You can check out e.g. https://support.mozilla.org/en-US/kb/thunderbird-telemetry.
I typically opt out of telemetry data these days, having been burned a few times.
@jeena @oi_dude Well, I mean, there was Foxstuck…
https://www.theregister.com/2022/01/18/foxstuck_firefox_browser_bug_boots/