@TeamYouTube today I was browsing my second channel and saw channels that I was subscribed many years ago and channels that I was never subscribed at all. On some of them notifications where turned on. Why????
Do you have third party extensions installed? If so, try disabling them, as they may subscribe you to channels without your permission: https://yt.be/help/2abj . Also, if you're using a shared device, sign out of any Google services when not in use. Keep us posted.