if you have two monitors with different native scales, then immediate viewports will cause the text to look messed up for the parent viewport:

I'm not sure why this is not a problem for deferred viewports; it's likely some state that is not properly restored when switching to/from an immediate viewport child.

The solution requires having one Fonts per specific pixels_per_point in Context.
We also need to do book-keeping of changes to the font atlas texture in a new, better way.
We really should use different font ids for the textures for the different pixels_per_point, but that will require a pretty deep change.