Hello,
In a floating menu item, i use "defin min and max width and height in pixel" size mode and put a min height and max height.
Later, I change the mode to "fit content".
The height of my content is now the min height set in the previous mode. If min height was 0, i can't see my item. I'll add screenshots later if necessary. My item is a web view.
For webview items "fit content" probably doesn't work at all as they are always scrollable, thus all content can fit in 0px 
So better continue to use the other mode for webviews.
If I understand correctly, a consequence is that it is impossible to have a web view item with dynamic height?
correct - unless you call some java script from the loaded website to change the size (I can post an example if this is an option)
I don’t think there is a good way to „guess“ what the best display size for a webview would be.
You're right that it's not "guessable" easily. You could sometimes take the width/height coming from sibling item on the menus (if they are not webviews, you could take the width in a column list, the height in a row). But the current behavior relying on an option set in another mode is a bug imo. I think there should be specific params for webview size.
I'm really interested with your JS. Do you do it by simply setting the body size?
Thank you for your work and your reactivity here, it's really enjoyable.