Both Itch (3 MB) and this forum (4 MB) have low filesize limits that are easy to hit real fast.
Now in another program I made I work with GIF making API, and it has no way to know the filesize before hand so I accept if there's no way to actually do this...
This is a great suggestion. If filesize cannot be figured out, then a way to save only the last 10,20,30,60 seconds might be a way around it?
Until then you can easily post-process your gif to trim it down to size: Post-processing Animated GIFs I used this approach for the Daily Driver trailer.