The RetroTink 4K would probably be the best option, but it's quite expensive. I don't own one mind you, just going off the specs and what other people in the community have commented.

Personally, I'd just get a separate monitor for DOS and call it a day. The ProArt is fantastic for Win9x and WinXP gaming at native 1600x1200 using a simple DVI to HDMI adapter, or even plain DisplayPort for XP era cards. If playing games in lower (non-native) resolutions, use a VGA connection to reduce blurring and adjust the sharpness to your liking.

BTW, with a simple INF modification, you can get the ProArt drivers to install on WinXP and Win9x, including the correct color profile and all.

I use ossc for retro PC with VGA connection for connection with a modern monitor and I'm satisfied. With a RetroTink 4K you can have better quality and an upscaling to high resolutions like 1440p and 2160p, but Is very expensive. I wanna buy that but I live in Italy and, with fee, vat and shopping, the price reach about 800 USD. Ossc for my demands is a good compromise.

Thanks for all the info. Yeah RetroTink 4K is too much. I’ll use a separate CRT for the older stuff.