In previous versions of Simulator.app, you could drag an unsigned iOS .app bundle onto the Simulator screen to install it. This was useful functionality to allow for more easy distribution of simulator-only builds within a team without needing to worry about signing and distribution. This functionality appears to have been completely removed in Device Hub which is a shame.
Simulator builds are signed, they’re just signed with an ad hoc [1] signature:
% codesign -d -vvv Test848739.app
…
CodeDirectory v=20400 size=315 flags=0x2(adhoc) …
…
You are right that Device Hub doesn’t support dragging in an app to install it. I think we already have a bug on file requesting such support (r. 179108532), but if you want to be sure you should feel free to file your own.
One alternative is to install the app using simctl:
% xcrun simctl install 'iPhone 17' Test848739.app
Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"
[1] This is different from the Ad Hoc provisioning profile used for Ad Hoc distribution on iOS.