Hi Handi,
Greetings from Syncfusion support,
We have validated your reported query. If the SfDialog is rendered based on the body, the height and width will be adjusted to the full pageview. If it is rendered based on the specific target, the dialog tries to adjust its height based on the target.
Could you please check and remove the target to the dialog while showing a dialog in full-screen mode?
Regards,
Indrajith