Is it possible to make a fast UI on say, an ESP32?

Wish I knew... I'm half way towards looking for companies who make white label android devices for a project of mine... I originally wanted to go stm32, but as soon as you add a touchscreen and want a responsive gui, my only options seemed like "smart displays" with pre-rendered ui graphics, or a full blown arm device. /shrug

Now I am curious what you're working on :-)

Well it runs at 20 Mhz, like a Motorola 68020 (Apollo DomainOS), so I would say, yes.

Microsoft has difficulties drawing (rounded) rectangles at 2 - 4 GHz but that's another issue.

But Motorola 68k in say... the Amiga (I don't know Apollo) would have additional chips for sprites and blitting, right? And the ESP - despite being extremely fast, doesn't have that extra support. So you need CPU... + tricks, DMA, triple buffering etc

Where are you getting 20MHz from? The OG ESP32 is a dual-core 240MHz micro...

I've been looking into this recently. It seems to be possible with the right kind of controller: https://www.youtube.com/watch?v=ZWtTmmne6Bo

Also the newer esp32-p4s have MIPI DSI onboard which apparently can do smooth HD.

Yes, see MS-DOS games. Now skills to do it 30 years later is another matter.

Is it possible though? I have never seen an LVGL demo (just plain C) able to present a demo or animation that is as "smooth" as a MS-DOS game on say a 486. Not that the 486 was butter smooth but it's not quite there. Maybe its the interface for the screen?