You could technically get 1024x768 (with really bad flickering) on anything with an AGA. Check out e.g. https://aminet.net/package/driver/moni/WBHacksAGA or https://aminet.net/package/driver/moni/HighGFX40_6 . The only high-res Amiga I saw at the time was an Amiga 4000 (it wasn't mine, but I had pretty much unlimited access to one at $parental_unit's workplace, where they had some fancy multimedia lab that generally went unused), but I expect the Amiga 1200 could do it, too. The flickering was pretty terrible but I was a kid and I had good eyes :).
HighGFX was actually popular (and useful) enough that it caused a bunch of "flickerfixer" hardware to sprout in the mid/late 90s but I've never used/seen one.
What Amiga did you have?