I swear Lemmy comments for YouTube had a feature that let you open it for any page, but it seems the GitHub and Firefox page been deleted.
Edit: Looks like I’ve still got a fork: https://github.com/Steve-Tech/Reddit-Comments-for-YouTube (it says Reddit, but works for Lemmy too)
Also if you tap on the ‘kebab’ menu and press
View Source
, you can copy the message.