[gilgoomesh]

Running an older version of macOS, which supports older versions of Xcode and then using that to run older iOS simulators.

[kuon]

Isn't the simulator not a VM? I thought it was more something like wine.

[plorkyeran]

Correct, the simulators run regular macOS processes that are linked against a different set of userland libraries than usual. No virtualization involved.

[ajmurmann]

Could I run an older version of macOS that still ran 32bit apps?

[jamesy0ung]

macOS Mojave is the last version to support 32-bit applications. It only runs on x86_64, so you'd be emulating it, not virtualising.