iOS

Official:

SponsorBlock supports https://m.youtube.com and can be used with the Safari extension (This does NOT work in the YouTube app).

https://github.com/ajayyy/SponsorBlock/wiki/Safari

3rd-Party:

App Store:

Yattee is an open source Invidious-based 3rd-party YouTube client.

Jailbreak:

SponsorBlock can be used on the official app using iSponsorBlock by @Galactic-Dev.

Sideload:

uYouPlus is a pre-packaged IPA with iSponsorBlock and other tweaks pre-installed.

Since this involves downloading a patched version of closed-source software, you should be wary before doing things like signing into an account.