Most notebooks, including the HP models, can function in mains operation even if the battery is defective. There is no general firmware lock that prevents this. However, there may be differences depending on the model and firmware version. If you have problems, I recommend consulting the official HP documentation or customer service.
The difference here is the display. The 819J8EA#UUZ has a much better panel with up to 1000cd/m² brightness and the device with the manufacturer number 5Z4C8ES#UUZ has a maximum panel brightness of 400cd/m². The following link leads to the manufacturer data of the product family: HP Dragonfly G4-13.5-inch notebook - technical data
Manufacturer data configuration 819J8EA
Manufacturer data configuration 5Z4C8ES
Attention: it is NOT a convertible! I have therefore returned the one I bought and bought it instead of the HP Spectre x360 Laptop 14-ef2799nz, which is a convertible and comes very close to the Dragonfly. However, it does not have mobile connect.
Thank you very much for pointing this out. We will gladly forward this internally to the responsible department and hope that this will be adjusted in a timely manner.