We have heard previously from the developers of Geco Midi that there is an issue with using this application on OSX Big Sur and that there are no current plans to address this in it's current form.
Please be aware that MacOS 10.14.6 is the last MacOS version to offer 32-bit support so you will also find that the existing applications written for 32-bit will no longer function with OSX Catalina, Big Sur or Monterey.