Wii to monitor, input not supported?

I connected my Nintendo Wii (2006) to my monitor with an HDMI adapter, the picture works well and I can play everything. The problem is that there's a small blue window flashing all the time saying "Input not supported". I have tried all the settings on the Wii, but do not really dare to change my monitor because the controls are completely confusing. Would be nice if someone can help me.

Time in the manual of the monitor looked? That's what they're there for!

I tried everything on the monitor, it is still there

What says the manual for this error?