robske_110's response was very helpful, but two notes: robske_110 missed "Platforms" in the directory path: It's Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport/14.5 Be sure to use the Finder to copy the directory. I used the command line the first time (sudo cp -r …), and Xcode didn't like it. I don't remember if it was a different error message than the unsupported iOS version, but it didn't work. (Yes, I quit Xcode before copying, then started Xcode again.) After doing the same thing through the Finder, it worked. The next time running the app from Xcode still took a little extra time; it said something about copying cache files to my phone; I assume that's related to the 14.5 stuff I just added with the above instructions. Also, ferFrassia mentioned 14.5.1 vs. 14.5. It looks like that DeviceSupport directory only has X.Y versions, not X.Y.Z. My iPhone is currently running 14.5.1, and copying the 14.5 folder fixed it (using Xcode 12.4 under Catalina/10.15.7). Thanks, all (especially robske_110) for the help!