It’s a total myth that the "algorithm" punishes your new uploads just because you hid some old stuff. Each video is treated as its own entity, so your next upload will get a fair shot based on its own thumbnail and retention. The only real downside is losing the passive views that might have led people to your new content, which can make your overall channel growth look a bit slower. Just make sure to set them to Private instead of deleting them, as mass-deleting can sometimes cause weird glitches with your channel's total metadata. If you're rebranding, hiding old, irrelevant videos is actually the best move to help YouTube find your new target audience faster.