The problem for me (NVDA/Windows) seems to be that you have an outer div with an aria-label. I believe that in most screenreaders, this is not an annotation of the contents, it’s a replacement for inaccessible content. At least, the aria-label is the only thing that’s getting read for me.
Here’s a recording of the spoiler in this thread: reading the time scrubber at the bottom of the video, then a blank (dunno what that is), then the visible spoiler (“button expanded hide content”) and then the “2 replies” dropdown.
Note that if I use NVDA’s debug feature and mouse over the expanded text to read it, it does read. But I haven’t found any way to get it to read the text without using the mouse. So that doesn’t seem to be a valid way to test whether it’s actually accessible…