Regular YouTube works as is (but has performance issues on my weak phone.)
It's m.youtube.com that seems to require the DRM thing, at least for me. Have you tried that?
m.youtube.com works fine in both Epiphany and Firefox on my Librem 5 with PureOS.
m.youtube.com works fine in both Epiphany and Firefox on my Librem 5 with PureOS.