Fidelity's lack of adequate support for Active Trader Pro on macOS
There was an older post regarding this at https://discussions.apple.com/thread/250072374, which concluded the issue was that ATP is 32 bit. If you have upgraded to Catalina, it forces the install of 64bit apps only (according to what I was told by Fidelity). Because of this, they now offer a 64bit Mac version at the following URL: https://www.fidelity.com/webcontent/CodeweaverInstaller/ActiveTraderPro64.pkg.
WARNING: I obtained this link from the IT support team prior to it being officially published on Fidelity's website. This installation currently takes a long time as they have not flushed out all of issues with distribution. It also downloads the Microsoft .NET framework to allow ATP to run on the Mac. After the installation is complete, this version of the download still warns that it is 32bit and cannot run, just click OK as this warning dialog has not yet been removed from the application.
Good luck!
[This is a Direct Download Link]
MacBook Pro with Touch Bar