Thanks to those who replied. It looks like pi-hole doesn't block YouTube ads on mobile - and any other solutions (blocker, or non-official app) are Android only

Thanks to those who replied. It looks like pi-hole doesn't block YouTube ads on mobile - and any other solutions (blocker, or non-official app) are Android only. Looks like the best solution might be to use a web browser on iOS - and visit one of these sites: https://invidio.us https://invidio.us https://www.layluh.com https://www.layluh.com