Likely something on my end as 5 months later, without any updates, it works.
Although it also might’ve been something on itch’s end.
On further inspection none of my extensions are working, please disregard what I said before. I probably just imported them wrong. With this one and a couple of the others it also said “Error parsing JSON file: unexpected end of input” which lead to me opening the .aseprite-extension files with winrar and manually installing them.