I immediate recognize the first clip as the Dawn Of War intro. The third is from the Amazon produced Secret Level 40k episode. Second video I'm unsure of off the top of my head, I think it may have come from something relating to one of the Mechanicus games.

These are just part of the flood of never ending low quality content in YouTube shorts (not just 40k shorts, but shorts overall). Channels taking official animations, slapping some dumbass text and music over them and calling it a day. GW defends their IP (sometimes overly heavy handedly), but they realistically can't and aren't going to go after every single shorts channel.

My solution would be to stop watching shorts.