Welcome to the internet. Have a look around.

Jokes aside, nothing you can do to stop it. You can mitigate it by using non-chromium browsers, blocking cookies, using adblockers and fiddling around in your google settings page.

Several possible reasons, so I’ll order by likelihood, and multiple answers may be compounded together as correct:

1. You’re mistaken on how much space you had, I dont see a reason for you to look at the exact number before shut down and then again on log in, unless you were expecting something.
2. You really need to clean temp files
3. Windows, driver, software, game updates/ leftover files
4. Onedrive or another cloud sync software auto downloading stuff
5. Something you’ve downloaded recently that actually used a lot more space than you anticipated (download size do not correlate to disk usage, compression is ubiquitous over downloads)
6. Possible malware.
7. Hardware failure (corrupt file table or corrupt files creating bad reads, or sectors too damaged to use)

Not that I know off. Plenty of FOSS browsers.

the whole point of FOSS is that you can literally see the code and decide if you’re ok with what it does, and even change it and recompile if you want.

People need to understand this already: is a piece of software free? The product is you.

Simple as that. If you’re using a non-FOSS software that is free, it is gathering your data and profiting off of you. Period.

Dont want that? Dont use that software.