I read somewhere that Euronymous also idolized Nazism as well as the USSR (I think he was a fan of Stalin mostly) so he had more of a fetish towards authoritarinism in general rather that Communism specifically, which obviously fits the edgelord aesthetic.
Varg was big into Nazism, as was Hellhammer and several other people connected with Mayhem. From how Varg says it, though, Euronymous was a tankie.
Most of Varg's video content got purged a few years back; here's an archived one where he (briefly, around 9-10 minutes in) discusses the political conflicts between Euro and some of their friends:
He went into it in more depth in other vids, but I can't find them offhand. IIRC, Varg's take is that Euronymous was basically Phil (only with more friends and a job): a tankie, homosexual, and all-around degenerate, obsessed with mallgoth/ edgelord fashion to such a degree that it aggrevated and alienated his peers, opposed to nationalism and racism, and who suffered from both bad personal hygiene and a lingering porn addiction (albeit guro and snuff/torture porn, rather than tranny/AGP stuff).
UNLIKE VARG, who was totally straight, not at all degenerate, and wore tasteful Fallschirmjager paramilitary camo gear, like a sensible grownup. (cough cough) Yes, Euro idolized authoritarianism, and he hung out with the fash kids (similar to Phil's occasional accidental fash slipups), but according to Varg Euro was a commited Communist LARPer, not a Nazi LARPer. He was the Antifa kid before it was cool.
Again, it's possible Varg's making shit up, or just doing a Rashomon and remembering things in a light most favorable to himself. But if Varg's
correct, then Euronymous was essentially a high-functioning version of Phil; the Phil that the worst part of Phil wishes he could be.