I confirm there is no overflow control available for Rich Text Asset, but there are maybe 2 workaround that might help you.
You can go with a Simple Text Asset with:
- checked “Adapt font size”
- same “Font size” and “Minimum font size”
- “Overflow behavior” set to “Scrollbars”
But in this case, you will lose the mixed font formatting feature.
Another way would be to go with an HTML Frame Asset and you will be able to fully control both the HTML and CSS, and deal with overflow exactly the way you want while still being able to format your content as you wish.
Keep in mind these HTML Frame Asset are a little bit ressource consuming so you may not want to have dozens of them in a scene.
Kind regards (and happy new year )