Since I could reproduce this issue on my local env(linuxmint 20, apache 2.4.41, enmod ssl+http2+brotli) by adding "AddOutputFilterByType BROTLI_COMPRESS video/mp4", remove it if you have such conf. (you must have it because of "content-encoding: br" in the response header on your site)
(btw, maybe it's better to submit a bug report because chromium edge has no problem with "content-encoding: br" for video/mp4)