

This may not be exactly what you’re looking for but have you considered using Firefox containers, automatically logging in to a different Google account for each container? I’m fairly sure this would work on mobile (probably only Android though), and is almost certainly more convenient and polished than a separate YouTube client.
Yes, although I recommend against using /c/ because it doesn’t actually link to the community. I also recommend against typing out the full URL (e.g. https://lemmy.ml/c/asklemmy) because it might cause issues for people in different instances.
The proper way to link to a community is !communityname@domainname.tld. For example, !asklemmy@lemmy.ml