Wow, OK—so this is why we do beta builds. 
When you press the spacebar or another key that isn’t working for you, do you hear the macOS system alert/beep sound, or does nothing happen at all in Capo?
Either way, I need to get some debug logs from you. Launch the Terminal app, copy/paste the following command, and press the return key to run it. When prompted, enter your login password:
sudo log stream --debug --predicate 'subsystem=="com.supermegaultragroovy.capo.CapoRemoteControl"'
Then, return to Capo and press some of those keystrokes—spacebar, command-arrows, etc. Back in the Terminal app, you should ideally see messages that look like this:
2025-03-31 10:08:00.235256-0400 0x41ade13 Debug 0x0 11232 0 Capo: (CapoRemoteControl) [com.supermegaultragroovy.capo.CapoRemoteControl:CapoRemoteCommandDispatcher] Dispatching: togglePlayback()
2025-03-31 10:08:00.340876-0400 0x41ade13 Debug 0x0 11232 0 Capo: (CapoRemoteControl) [com.supermegaultragroovy.capo.CapoRemoteControl:CapoRemoteCommandDispatcher] No commands for message: keyUp(space)
2025-03-31 10:08:01.471461-0400 0x41ade13 Debug 0x0 11232 0 Capo: (CapoRemoteControl) [com.supermegaultragroovy.capo.CapoRemoteControl:CapoRemoteCommandDispatcher] Dispatching: goToSongBoundary(beginning)
2025-03-31 10:08:01.542247-0400 0x41ade13 Debug 0x0 11232 0 Capo: (CapoRemoteControl) [com.supermegaultragroovy.capo.CapoRemoteControl:CapoRemoteCommandDispatcher] No commands for message: keyUp(command leftArrow)
2025-03-31 10:08:02.366250-0400 0x41ade13 Debug 0x0 11232 0 Capo: (CapoRemoteControl) [com.supermegaultragroovy.capo.CapoRemoteControl:CapoRemoteCommandDispatcher] Dispatching: togglePlayback()
2025-03-31 10:08:02.474421-0400 0x41ade13 Debug 0x0 11232 0 Capo: (CapoRemoteControl) [com.supermegaultragroovy.capo.CapoRemoteControl:CapoRemoteCommandDispatcher] No commands for message: keyUp(space)
2025-03-31 10:08:02.955027-0400 0x41ade13 Debug 0x0 11232 0 Capo: (CapoRemoteControl) [com.supermegaultragroovy.capo.CapoRemoteControl:CapoRemoteCommandDispatcher] Dispatching: goToNext(entry: bar)
2025-03-31 10:08:03.200510-0400 0x41ade13 Debug 0x0 11232 0 Capo: (CapoRemoteControl) [com.supermegaultragroovy.capo.CapoRemoteControl:CapoRemoteCommandDispatcher] Dispatching: goToNext(entry: bar)
2025-03-31 10:08:03.235381-0400 0x41ade13 Debug 0x0 11232 0 Capo: (CapoRemoteControl) [com.supermegaultragroovy.capo.CapoRemoteControl:CapoRemoteCommandDispatcher] Dispatching: goToNext(entry: bar)
2025-03-31 10:08:03.267735-0400 0x41ade13 Debug 0x0 11232 0 Capo: (CapoRemoteControl) [com.supermegaultragroovy.capo.CapoRemoteControl:CapoRemoteCommandDispatcher] Dispatching: goToNext(entry: bar)
2025-03-31 10:08:03.300570-0400 0x41ade13 Debug 0x0 11232 0 Capo: (CapoRemoteControl) [com.supermegaultragroovy.capo.CapoRemoteControl:CapoRemoteCommandDispatcher] Dispatching: goToNext(entry: bar)
2025-03-31 10:08:03.334141-0400 0x41ade13 Debug 0x0 11232 0 Capo: (CapoRemoteControl) [com.supermegaultragroovy.capo.CapoRemoteControl:CapoRemoteCommandDispatcher] Dispatching: goToNext(entry: bar)
2025-03-31 10:08:03.368339-0400 0x41ade13 Debug 0x0 11232 0 Capo: (CapoRemoteControl) [com.supermegaultragroovy.capo.CapoRemoteControl:CapoRemoteCommandDispatcher] Dispatching: goToNext(entry: bar)
2025-03-31 10:08:03.383807-0400 0x41ade13 Debug 0x0 11232 0 Capo: (CapoRemoteControl) [com.supermegaultragroovy.capo.CapoRemoteControl:CapoRemoteCommandDispatcher] No commands for message: keyUp(rightArrow)
Please copy the messages and then paste them in here for me to take a look at.
If there are no messages:
If nothing appears in the Terminal while you press keys, try quitting and re-launching Capo while the log messages are still running. At the very least, you should see the following messages (or something like them) on launch:
2025-03-31 10:11:37.389590-0400 0x41d8470 Info 0x0 14404 0 Capo: (CapoRemoteControl) [com.supermegaultragroovy.capo.CapoRemoteControl:First-Time Initialization] First-time initialization already completed
2025-03-31 10:11:38.119404-0400 0x41d8357 Info 0x0 14404 0 Capo: (CapoRemoteControl) [com.supermegaultragroovy.capo.CapoRemoteControl:CapoRemoteCommandDispatcher] Bindings successfully initialized
2025-03-31 10:11:38.778057-0400 0x41d8357 Debug 0x0 14404 0 Capo: (CapoRemoteControl) [com.supermegaultragroovy.capo.CapoRemoteControl:CoreMIDIMessageProvider] Successfully created MIDI client
2025-03-31 10:11:38.782294-0400 0x41d8357 Debug 0x0 14404 0 Capo: (CapoRemoteControl) [com.supermegaultragroovy.capo.CapoRemoteControl:CoreMIDIMessageProvider] Successfully created MIDI input port
Let me know if even these messages aren’t showing up for you. Thanks!