@SimonSchütte_ct mentioned in Feature class name starting with a number:
There is no feedback on why you can´t type in a number:

Ideally switch Alias and Name fields and add a "copy values over" button.
If the Alias starts with a number, inform the user that the Name cannot start with a number and suggest an alternative such as underscore number by default. Bonus point if the ArcGIS Pro Settings get an entry to specify the default prefix for Names that would usually start with a number %prefix%

Could Pro be enhanced so that it explains to the user that FC names that start with a number are not accepted? Not just documentation, but a warning right in the software.