I've installed Rider EAP on a couple of Macs, and when I load the uproject I see Mac and tvOS platforms, but not an iOS platform.
Both machines are using a UE4.27.2 Chaos source build (1 lightly modified, the other unmodified). I'm seeing this for both our large in development project and with the UE4 template projects (Third Person Shooter, C++). iOS is enabled in the supported platforms in the project, and generating the xcworkspaces with UE creates workspaces with iOS targets supported.
If I build and launch the editor from Rider, I can build/package iOS apps from within the resultant editor.
This is across 2 M1 Monterey Macs using the M1 app bundle, and 1 Intel i7 Mac on Big Sur.