Video with transparent background file-size issue
Transparent video on the web is possible, but it's going to only work for users with modern browsers.  You'll need to export in two different codecs - one for Chrome users, one for Safari.
From this site:

Safari supports HEVC with alpha, Chrome does not.
Chrome supports VP9 with alpha, Safari does not.

You need to export an HEVC with alpha channel for Safari.
You need a .webm VP9 codec with alpha for Chrome.
The animation codec you've exported at is not designed for web publishing.  It's a lossless very large codec designed for editing or archiving your finished project before you use it to make a smaller lossy version to go on the web.
This is how to make the webm using ffmpeg
ffmpeg -i &quot;movie-prores.mov&quot; -c:v libvpx-vp9 movie-webm.webm

I would recommend also exporting a &quot;fallback version&quot; for browsers that can't cope with transparent video (as a normal h264 mp4 or webm).