Valhalla runs on DX12. Some older trainers struggle with this; try launching the trainer after you have fully loaded into your save game rather than at the main menu. Reliable Trainer Sources for v1.7.0
You can farm skill points by repeatedly killing the "Elder Lynx" in certain boss areas and leaving the zone to respawn it. assassin 39s creed valhalla trainer 170 work
Yes, but with significant caveats.