Very slow second monitor

I am using a M1 Macbook Pro (32 Gbyte RAM, 2 Tbyte SSD) for editing my photos in LR classic (Abo version). I am using LR with the MBP monitor as standard monitor for a small display of the image plus menue and a BenQ SW270c as second monitor (in loupe mode) to have a close look at the photo...

When I perform adjustments of, e.g. Temp or Hue, the image on the MBP monitot changes fast, while there is often a delay of 2-4 seconds after also the image on the BenQ270x changes its appearence. This is very annoying...

Is this normal (=very disappointing) or am I doing something wrong and need to adjust something?

Thanks, Wolfgang