Your software
My Mautic version is: 3.0
My PHP version is: 7.3.20
Your problem
My problem is:
When editing an email in 3.0 + and trying to add an new or saved image into the mail, the new file manager does not save the selected image into the email.
Just added this on Github but in case other folk are needing a workaround, this issue happens with image slots, you can add an image to a text slot without having this problem. So that might be a viable workaround until we get this addressed