Bookmakrs - Synced Bookmarks - Synced with what?

Relatively unimportant, but I've always wondered: when managing bookmarks, the entry 'Other favorites' shows a sub folder 'Synced Bookmarks'.
In my case, there are 4 familiar entries in there. However, should that folder sync with my smartphone, then Edge there has 9 entries on the 'Home' page (i.e. the one after launch).

I know, it sounds pretty much as a newbie question, but I am not sure what is actually being synced from where in that folder.

I know that Firefox and probably the other browsers use a bookmark server sync service. Since I don't care to use such a service as I think it invades my privacy I don't know much about it or use it. But on its face I think that's what you're seeing there.

I guess it's a nice feature for the layman - someone who's not too computer savvy, but with convenience comes a bit of a privacy invasion. Especially, Especially! if a court order is issued to retrieve all those bookmarks for public viewing. Here's an example: I have hundreds of bookmarks relating to hacking things. Not because I do so, but because I'm interested in the subject matter and cybersecurity. In the wrong hands the low IQ among us will think I'm some kind of black hat hacker extraordinaire or whatever and burn me at the stake. The avatar I use now would solidify that. Also, you can get a glance at what people are looking up and how people think and all that crap. Like a search engine query history.

So every once in a while I chose to backup my bookmarks to an encrypted 7z archive and manually backup that file all over the place...