Put the Super72 monitor driver in DEVS:Monitors and reboot. You can then select 800×600 super72 super-high res laced.
Or set your Workbench to PAL super-high res laced (1280×512). You can use Overscan preferences to make that slightly larger. I'd recommend doubling the height of the emulation window if using that mode.
If you install
the HighGFX monitor driver you can do 1024×768.
Finally (does FS-UAE support this?) you could use A2024 modes, 1024×1024 but only in four shades of grey.
That's all the native chipset mode options I think. For larger screens you can install Picasso96 more much larger resolutions. 3840×2160 Workbench is possible there.