From a quick online search, it seems Borderlands 3 has had mixed success on macOS since its initial launch. Since Epic is the only source for the macOS version of the game you need to open a support ticket with Epic. It is up to Epic or the Epic Store to help you run the game on its supported platforms.
Like I said, you may find some tips & suggestions by looking at the Borderlands 3 game community & forums related to the macOS platform. I'm sure there will be some people there who are also having similar issues unless there is something unique about your system's configuration. There is a chance the issue could be related to one of dozens of new security features within macOS. Apps should inform you of this, but sometimes it is possible to not notice some notifications alerting you to the need to modify certain security & privacy features.
You may want to test things out by booting into Safe Mode, but I don't know whether this will be supported by the game. If you are running any anti-virus apps, cleaning/optimizer apps, or third party security software, then uninstall them by following the developer's instructions.
Since it has been a month since your initial post here & I'm the only one to respond, it doesn't seem likely anyone here knows anything about Borderlands 3 on macOS, although it seems eight other people are also having an issue as shown with the "Me Too" count. If you do find a solution or anything which helps, please update your thread here so it may help someone else who finds this thread since at least eight others seem interested in an answer.