Something weird happens sometimes is that my PC boots into the old windows on another installation, by itself, despite setting priorities in BIOS.
Remove the boot files from that drive.
It's probably getting confused when a update is installed and redoes the boot record and bios and gets it wrong. You may get away with just removing the boot partitions (uefi/gpt) but there's times (Bios/mbr usually) where the only fix is move all the data you need to keep off of it, delete then rebuild the partition then put the data back,
Warning!!!! Remove that drive first and make sure the system still boots before you do this!
If it does, feel free to remove the boot partitions, if it doesn't you can try a Windows install disk and repair it or put the drive back and live with it but don't just start deleting partitions and files.
The PC goes smoothly after a restart, but then goes complete **** after about 10 hours of usage, almost unusable and super laggy. I work with many internet tabs open and I wonder if that is the cause of the issue. I just have very strong hardware so... seems odds that this should be the case.
Hardware doesn't matter, at least not to the extent people think*, this is an I/O issue (and possibly a memory leak problem and even more likely a data harvesting problem**)
More ram and more cores help but only to a certain point, people think of ram and cores like roads, 6 lanes means 6 cars at a time, I/O however is more like the number of people in those cars and your cpu/ram can only process so many people at once, regardless of the number of cars. It is a hardware issue and it can be fixed but we're talking Threadripper and Xeons with 4 or more channels of memory and such with super high I/O, not just simply more cores or more memory.
The fix I tell people is multiple browsers.
Not two Chrome based, it needs to be different architectures, not only so they aren't fighting over resources but also so the system sees them as different and force them to play nice with each other and not hog everything they can. Not a perfect fix, but can help greatly.
Note that this is a bit over simplified and not very accurate but should get the point across.
*We're also reaching a point where the software itself is also a bottleneck, tricks to make old slow hardware seem fast is now holding back our speeds. I know, "what Intel giveth Microsoft taketh away". This is different. It used to be the system would do other things while waiting on data to be fetched for example checking network connectivity while waiting on the desktop files to be fetched by the drive. Today the system asks for the desktop files to be sent then leaves to check network connectivity and the drive immediately comes back with the data going "where'd you go?" In extreme cases the cpu takes so long to get back to the drive that the drive has dumped the data because it thinks the CPU has decided it was no longer needed, this is an actual problem in data centers right now.
** I suspect trackers from closed pages/tabs are what are not clearing from memory, likely by design.
But ever since I updated to windows 11 I seem to have problems constantly.
Win11 is a sh*tshow.
I honestly have little hope it will ever be "right", just look at the troubles Win10 still has. How many years have they had to fix Win10?