https://www.diskpart.com/articles/syste ... -3889.html
Leaving this for future reference as it worked in my case.
All the other tutorials failed.

These steps in particular:

bcdboot c:\windows /s c:

diskpart
list disk
select disk n (where n is the disk number of the system drive)
list partition
select part 1
active (the correct message should be: DiskPart marked the current partition as active)
exit (leave diskpart)

Looks like a fresh install is still necessary as the antivirus doesn't load and I cant seem to uninstall it. Just loads forever.

Interesting. I've used diskpart making bootable USB drives to install disk images and stuff. Have you tried booting in safe mode to see if you can remove the antivirus? Still, if things are that wrecked, a clean install is usually best.

Well the problem i had to circumvent was that:

bootrec /fixboot returned access denied.
bootrec /rebuildbcd returned 0 windows installations found.

attrib bcd -s -h -r had no effect as well. the attrib bcd part was a bit longer but i cant recall it.
Basically what this does is remove read-only and hidden from the boot partition drive.
The drive is now visible under "This PC".

So the commands from my previous post had the effect that the system partition is now used to boot windows.
In the end it is not really a fix. It is a method to bypass broken bcd. At least that is what i believe it is.

Ah, ok. Thanks for the explanation. It's been a long time since I've messed around with Windows boot files.