So, I think I finally solved the reason for crashes.
It was Rivatuner Statistics Server. The RTSS recently started giving error message about "Some system components cannot be hooked right now." This error message started popping up after Windows update.
I thought that closing the software would really close it but Task Manager revealed that it still autostarted itself. This prevented the updating of the RTSS, too, as the update wouldn't finish if RTSS was running.
After disabling the "autostart with windows" from RTSS I managed to update the RTSS to the latest Beta version, which has fixed the "Some system components cannot be hooked right now." error message. This seems to have fixed the crashing of AC Valhalla, too.

Oh man, it was too early to celebrate.
The crashes continued! After my last session I wrote that everything seemed to work. How wrong I was!
Now when I tried to play, the game crashed after 2 minutes of playing, twice. There really doesn't seem to be any reason for crashes. It might crash four times today and work perfectly tomorrow. I don't get it.

The game always crashed to desktop without error message and uplay wanted to send a crash report.
So, I did the Verify game files from uplay. Then I shutdown RivaTunerStatisticServer, MSI Afterburner and SteelSeries Engine from the background.

When I started the game next time, Uplay seemed to install VCRedist_2019 or something first, I didn't manage to see it properly. After that, there was no more crashes and I managed to play through the Bloody Welcome quest and a couple of side quests too without any crashes.

Problem solved, I guess, although I'm not entirely sure what helped. Probably the Verify game files option, as uplay installed something new after that.

I can't play the quest Bloody Welcome. It crashes constantly, mostly outside the church but also inside it.
This happens on versions 1.1.1 and 1.1.2.

PC Specs:
Ryzen 7 3700x
MSI Gaming X Trio RTX 3070
TUF GAMING X570-PLUS
1TB 970 EVO Plus SSD
16GB HyperX Fury DDR4 3200MHz