I've never paid that much attention to retro hardware - I still have a lot of the originals in my parents' garage.

I just moved, which gave me an opportunity to give all the old Rock Band instruments that were too loud for my last apartment a fresh try. It's disappointing how bad RCA-era systems like the Wii looks on a 4K OLED. The upscaling is blurry as shit.

I've been trying to get all my songs imported into YARG (an open source Rock Band clone), but if I can't get that working, maybe I should get a scanline generator. (It applies a filter to the video to replicate the look of a CRT.)

You can get better video output from the Wii than RCA. It won't be 4K but it will be much sharper:

https://electron-shepherd.com/products/electronwarp

There was also an official component cable which would look much nicer than the composite that the Wii comes with. But your 4K tv almost definitely don't have component input.

Thanks for the tip!