Besides the ones already mentioned:

• The FSF has some channels at https://framatube.org/a/fsf

• There's a bunch of KDE related channels at https://tube.kockatoo.org

• Blender has several channels at https://video.blender.org

• https://peertube.touhoppai.moe/a/shichimi has Krita tutorials from the creator of the Pepper and Carrot webcomic.

• https://tilvids.com/a/martin_owens from someone who works on Inkscape.

• https://tilvids.com/a/togglejam looks at the science behind fictional games and shows.

• https://diode.zone/c/andrewtropin has a bunch of scheme and guix related videos

• There's some anarchist channels on https://kolektiva.media like CrimethInc and subMedia.

A couple of gaming related accounts/channels:

• https://subscribeto.me/a/gbryant

• https://peertube.linuxrocks.online/c/boilingsteam