This happened to me several times already: I upload my game for Windows, Linux, macOS and WebGL at once. I edit the game page to reorder them. At the same time, I enable HTML play and mark the WebGL zip as playable in browser.

I save and test: error, no index.html found.

I check the uploaded file list again: the wrong file was selected to be played in browser, e.g. the Linux build.

The first time I thought I just misread the file name and selected the wrong file. After 2-3 repro, I can say it’s a bug.

It seems that marking a file as playable in browser uses its index, and reordering files via move up/down changes indices and somewhat the program doesn’t understand the combination of the two changes. Or, selecting file as playable in browser puts in to the top, changing its index to 0, but instead the first non-HTML file will have index 0 (in my case, the Linux build) and will be selected instead.

To repro, you need at least 1 non-HTML zip and 1 HTML zip, upload them together (I do it via butler), reorder them, and mark the second one as playable in browser. If it doesn’t repro, remove everything and try again, uploading them in a different order. You can also try with 3+ files, with a single HTML zip.