For YouTube, it’s probably not possible to not use its content, but you can try alternate front ends like Piped (and its wonderful Android client, LibreTube, if you’re on Android.)

For Gmail, not sure if this works for you but I set the vacation feature to reply to every email I receive notifying them of my new email. I switched to Vivaldi Webmail (Proton doesn’t let you use 3rd party clients w/o a subscription plan btw, I’d switched to Vivaldi first so not a major thing for me) but Skiff (paid) looks good, Kagi Search is planning an email service, Tutanota has an email service, and I guess you could self host. While you transition, use a client that lets you have a unified inbox (K9 works on Android) and just have both logged in.