Besides the ones already mentioned:
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The FSF has some channels at https://framatube.org/a/fsf
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There’s a bunch of KDE related channels at https://tube.kockatoo.org
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Blender has several channels at https://video.blender.org
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https://peertube.touhoppai.moe/a/shichimi has Krita tutorials from the creator of the Pepper and Carrot webcomic.
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https://tilvids.com/a/martin_owens from someone who works on Inkscape.
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https://tilvids.com/a/togglejam looks at the science behind fictional games and shows.
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https://diode.zone/c/andrewtropin has a bunch of scheme and guix related videos
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There’s some anarchist channels on https://kolektiva.media like CrimethInc and subMedia.
A couple of gaming related accounts/channels:
The creator of pixelfed is working on a tiktok alternative loops, although for now it’s in private beta.
For a starting point that is available now, you could look at Pixeldroid, an open source pixelfed app.