@jldb I had a similar problem in Xcode 12.3 when working with one of my projects. Basically, the Debugger would not Stop on the Breakpoints I enabled in the gutter in one project, but it worked fine in other projects... I finally checked the Project Scheme and noted that the project with the problem did not have the "Debug executable" checkbox selected. Once I checked this box the Debugging operation worked normally. I hope this post helps anyone with a similar issue. Cheers, Mark