It’s not an easy answer, but the best way I’ve found so far is to use GrayJay.

If I find that one of the content creators I follow on YouTube happen to post their content on any other platform, I switch my subscription to that platform.

Besides YouTube they support Nebula, Twitch, Odysee, PeerTube, Dailymotion, Bitchute, Kick, BiliBili, Rumble, Patreon, and more.