Before the launch of macOS Sierra in 2016, you could simply turn on an option to allow apps from ‘anywhere’ and run apps by unidentified developers. With the launch of Apple Silicon and Big Sur, macOS has made it even harder to run a third-party app. “Well, it’s my device. I was experiencing this problem after downloading High Sierra to fix a friend's Mac. I found Rick's solution worked for me, but I've added a few more steps. Click the symbol in the Menu bar. Hold down Command + R to boot into Recovery Mode. Click Utilities.