I am experiencing crashes very quickly after game start as well (maybe 5 mins into it), but this happens when I use a CoSMOS table or a CH trainer. I think Ubis most recent update introduced some changes that maybe tables/trainers hook into that puts wonkyness into the game for some people. I will do some testing without trainer (yuck..) and see if it is still unstable or not.
Previous game version ran flawlessly with CH trainer.
Windows updates the other day could have reset all your security settings to default and reverted any changes. Check your AV/security software make sure it's not blocking the trainer. CE being flagged/blocked is becoming standard practice for for a lot of game dev's, try using CoSMOS and convert the table to work with it, may have better luck.
If the game did update then be sure to report it. But I see AC Valhalla still shows last update on Feb 15th to 1.1.2 on the Ubi forums
1.2.0 update causes virus/trojan (windows defender)
File is clean. False positive.
Were the inventory options removed?
If an option was there in a previous trainer and not there in the current trainer, high probability it was removed.