For me, the issue was related to Rosetta. My Flutter project was originally built on an Intel-based Mac, but I’m now using an Apple Silicon Mac. Installing Rosetta resolved the simulator destination issue.

I followed the steps in this article:
Rosetta Simulator Run Destination not showing in Xcode 26

After installing Rosetta and restarting Xcode, everything worked — simulators were detected properly and the app launched successfully.