UMIDIGI F1 - No change of USB connection type possible

Just4Questions

Hello everybody,
on my F1 it is not possible to select the type of USB connection after it is connected to the PC. All selection fields are greyed out so I can not switch to the "transfer files" mode.
Tested with the current EU and Global version of the ROM in my preferred (German) language and in native English.
The only option for me was to set the default USB connection to "transfer data" in the developer options.
It would be nice to be able the settings on the normal way to do.
Does anyone have an idea for this? Thank you.