Scaling output to 4K monitor

[IRIS IT]

Hi,
we are using Veyon 4.5.1. The master screen is 1920 x 1080. The remote monitors are 4K (3940 x 2160). When the master is displayed in full screen on the remote monitors it is display as 1920 x 1080 in the top left of the remote screen. The resolution of the monitors cannot be adjusted. Is there any way for Veyon to scale the output to full screen?
Kind Regards
Robert