I'm not sure of your reasoning on "anything can be...".Yes, I suppose, but without elaborating further that doesn't explain why you're taking it to be circular, because I could have given some other description of what trends & goes viral on TikTok and you still could have said "Anything can be can be turned into that."
If we take it in the more formal logic direction you're going though it's all very simple and straightforward, here's the p & q -> r of things:
Algorithms of this sort work a particular way in directing next-video selection towards options with some characteristics similar to what the user has engaged with before. I'll stipulate there are lots of ways that can be done, time horizons and methods of weighting different factors but that's the broad strokes. Take this as premise P.
There are certain things that trend more frequently than others and they share some common traits, it really doesn't even matter what those specific things are, we can take this as an axiom without it being controversial.
Therefore, if anti-democrat content is disproportionate to pro democrat or anti or pro GOP, it isn't automatically thumb-on-scale, it can simply be that anti-democratic content has more similarities to what typically trends than those others.
This isn't circular. It's trending content is similar, anti-democratic content trends more often, therefore anti-democratic content can simply have been more similar to other trending things.
You're correct of course about Occam, but then your bring up that aspect of things was merely expanding on what I explicitly stated in my original comment when I said it didn't mean TikTok didn't tip the scales, only that such a thing isn't the only possibility. In short, it was clearly not stated as an "IIF/if-and-only-if" argument.
Going on to your For "arguably the opposite" final statement:
I think that too needs more little explanation. As-is, it sounds as though you're saying essentially "the fact that simpler explanations can be wrong is potential evidence for deliberate interference". That's a line of thinking when, offered without expansion, steps somewhere just adjacent of conspiracy thinking of the "the evidence is in the lack of evidence", and I doubt that's your intent, but I'm not sure either where that's heading otherwise.