> You can do the same thing with a vt220.

Can you? The last I looked at it (a year or two ago), the vt220 in MAME was just the beginning skeleton of an implementation, and it doesn't seem to have been touched much since then. A shame, because AFAIK no "terminal emulator" implements vt220-style sixels (which are different than than the widely-implemented vt4xx-style sixels).

I checked and it was actually the vt240. That one works.