This is the only suggestion that worked for me. Tested on Xcode 26.3 (17C529), macOS Tahoe 26.3.1 (25D2128). I had to make sure my SSH key, config file, agent, etcetera were all squared away on my machine and in Xcode's GitHub preferences first. Then: quit Xcode, run the suggested CLI command to update the defaults, relaunch Xcode.