The options for header fields are very limited when compared to Classic UI:

Current State (UCI)
High Density: Unable to edit fields at all
High Density, Flyout enabled: Unable to edit fields directly, chevron must be used to edit fields
Low Density: Fields are way too wide and even on a full hd, fullscreen browser window only 3 of the 4 fields are displayed.

Previous State (Classic UI)
Displayed all 4 fields properly, at an appropiate width, while the fields were editable without having to resort to a flyout.

Expected State (UCI)
a) In Low Density mode, Redesign where you align the asteriks (*) showing that a field is optional. This should be right next to the label text, not at the far right of the entire control
b) In Low Density mode, Redesign how you deal with field label widths as well as field input widths. Usually these are way over the top and do not consider their content at all.
c) In Low Density mode, all 4 allowed fields should be displayed at almost all times. When looking at the preview screen sizes, all 4 fields should be visible for both Desktop and Tablet width.
--> all of this would simply restore the features we've had in Classic UI, but MS Engineering does not consider this as feature gaps
d) Alternative approach: Make High Density mode editable without the Flyout by offering a switch "Read Only - Yes/No" for each field in the Header (alternatively a single switch for the entire Header, but that's just the lazy solution)

Suggested Improvements (UCI) over what Classic UI already had
a) Allow for more than 4 fields in the Header to be displayed without a flyout.
a.1) High Density mode could easily allow this, just make it dynamic like what you did with Low Density mode - but without the hardcoded 4-fields-limit.
a.2) Once the Classic UI Features are restored this should also be possible for Low Density mode