AMD ATI Radeon 5450 1gb Display Issue

I’ve installed an AMD ATI Radeon 1gb GDDR3 GPU on my manjaro linux 5.10-rt machine. It has display ports for DVI, HDMI and VGA. I can only use HDMI and DVI, because the VGA port doesn’t work for some reason. The Display app can detect it, but when I try to activate it I get the following error.

GDBus.Error:org.gtk.GDBus.UnmappedGError.Quark._gnome_2ddr_2derror_2dquark.Code2: could not set the configuration for CRTC 80

Please advise

Does it work with the normal kernel linux510 (not patched for realtime)?