A great way to demonstrate a bug or a problem is to record a video of it.
If you are a Windows user, you can click Win+G to open the "Game bar".
There you will find the built-in Screen recorder.

The video compression is good, but you will save even more space if you put the video in a zip file.
Example: a 40 MB video can shrink to 2 MB when zipped. Small enough to be able to attach in an email.