To be clear, the problem is still reproducible - If I close my browser, and open it again, it's still black until I open it in a new tab, after which it works as an embed as well, after I refresh this page.
Maybe it has some trouble downloading and caching the assets or somesuch, but works after getting them from the non-embedded version? No idea.
If I close the new tab (https://html-classic.itch.zone/html/11449738-1137422/index.html ), and refresh the embed, it is again black.
This opening in new tab does not fix it in chromium.
Both browsers show similar errors:
Uncaught TypeError: t.buttons[n] is undefined index.html:1:71307 Uncaught TypeError: t.buttons[n] is undefined be https://html-classic.itch.zone/html/11449738-1137422/index.html:1 ye https://html-classic.itch.zone/html/11449738-1137422/index.html:1 xt https://html-classic.itch.zone/html/11449738-1137422/index.html:1 pe https://html-classic.itch.zone/html/11449738-1137422/index.html:1 mc https://html-classic.itch.zone/html/11449738-1137422/index.html:1 update https://html-classic.itch.zone/html/11449738-1137422/index.html:1 update https://html-classic.itch.zone/html/11449738-1137422/index.html:1 Hi https://html-classic.itch.zone/html/11449738-1137422/index.html:1 Hi https://html-classic.itch.zone/html/11449738-1137422/index.html:1 Hi https://html-classic.itch.zone/html/11449738-1137422/index.html:1 index.html:1:71307