I don’t know that you need a semicolon but you could definitely use one, and that would probably be the best way. Semicolons are for when two complete sentences are related. But they can still be formatted as two sentences, or even the same sentence with a comma. Many sentences contain parts that could be standalone sentences. But reading back over the original sentence again I would probably say it can just be rewritten to be more straightforward.

“Another aspect to this video is that Somerset, when actually trying to write some of the material himself, produced complete garbage.”

Mostly I’ve just been reading a lot of philosophy recently which tends to run on a long and complex sentence structure that’s unnecessary and could be a lot simpler, so this kind of thing has been at the front of my mind lately. That’s probably the only reason I even noticed in the first place.