This is now officially being called “dustgate”. It is caused when dust (or other particles) get into the screen via the plastic cover (with macbook pro). These particles can then settle on the ribbon cable, and when the lid is closed, the particles can push into the cable and cause the tracks to break.
There has been a recent uptick in reports (on reddit and other sites). I’ll also note that I too have had it happen to my 2018 macbook pro just a few days ago.
Apple has acknowledged the problem (in that they fixed it in 2021) but have not yet offered a repair program for it.
I’m currently using my 2018 as a desktop machine, awaiting for the repair program.
In safari, each tab is a new private session, so there’s no way around it - unless you use something other than safari for private browsing.