I've now decided to start a collection of retro games and consoles.
And the first two I’ve bought are:
Choosing the Wii was an easy decision. It has some really great games (I actually owned one years ago), the graphics are still nice, and you can play Nintendo GameCube games on the Wii (as long as it's the right console version).
The Nintendo 64, or N64, was my second choice because I have great memories of "The Legend of Zelda: Ocarina of Time" and "GoldenEye" (and many other games).
Now it looks like a big mess :-D

But first I need to figure out what kind of other hardware I need. Upscaler, HDMI switch, cable management, and a new drawer for everything.
Connecting the Wii to an HDMI monitor was easy. I've got a Wii HDMI adapter from Amazon.
Amazon-Link: https://www.amazon.de/dp/B07BC96ZFM

But it's also important that you change your console display settings. Go to your settings and change TV-Type to EDTV/HDTV (480p) and also change the image aspect ratio to 16:9 (widescreen).
That gave me a much clearer image. Not perfect - but somehting you can live with (for now).
This is much more complicated. As I have a PAL version without any mod, you don't have the S-video signal. Or at least that's what I have read about it.
I tried the Kaico Analogue x2 HDMI Adapter, but as it only worked with composite output, the quality was terrible. Maybe it's a suitable option for NTSC versions.
After long research I found this video:
I am not sure why this cable is giving you a clear S-video signal (as the PAL version should not have it), but it works great!
So get this cable on Amazon for round about 10 € and use the S-video signal (the black cable). It's totally worth it!
Amazon-Link: https://www.amazon.de/dp/B01C575B6S
I will get myself a proper upscaler for better image quality. But first I need to do some research, as this topic is really complex (price vs. quality paired with the PAL version of the consoles), and I directly want to consider the SNES, Sega Mega Drive and others.
Stay tuned!