https://www.cnet.com/news/youtube-app-incognito-mode-browsing-history-leak/

You might not have to worry much longer about being judged for your YouTube viewing history. That's because the YouTube app is reportedly testing an Incognito Mode that won't keep track of your watched videos, as spotted by Android Police.

YouTube automatically saves your viewing history and ties it to your account. By doing this it can recommend videos or suggest ads, but sometimes you don't want that. Just because you watched one at-home pilates workout video (it was an accident!) doesn't mean you wan't pilates ads everywhere or for your suggested videos to all be people working out in spandex.