At @Trash80toHP_Mini's request, a thread about the HDMI scaler I found myself using to do vintage Mac stuff on a modern screen. It works, at least for me, really well and I'd recommend it to other folks as well. It is also not *that* expensive.
The model is Extron RGB-HDMI 300 or 300 A. I spent about £55 on mine from eBay UK, second-hand of course. At time of writing the cheapest on eBay US looks like about $35, so I may have slightly overpaid, but most seem to be $70ish. This,