From June 1st, YouTube will apparently claim the right to put advertising in all of the videos on their platform, regardless of whether the creator has enabled advertising on them. Will this effect the integrity of speedrunning submissions? I imagine it will be harder to validate a submitted time with advertisements popping up in the middle of a run.

Use an adblocker and/or download the VOD as well. First thing that comes to mind anyways.

@k-Patch 99% of people here use adblock from what I know. Also, if an ad pops up the middle of a run, you can just rewind and it won't play an ad again (from what I remember)

Ads stop a video. There is literally nothing stopping any verifier from verifying a run this way.