If you are impatient, or upgraded and realized your mistake too late (like me), here's how you can make your current driver run. It took me a couple hours to figure out, so hopefully will save you some time. I tried to make the description accessible to all, not only the computer-literate.
- 1. Install the latest available OSX 10.15 driver from Motu website (if you haven't already).
2. Restart holding down Command-R to reboot into Recovery Mode.
3. Select Utilities --> Terminal from the top menu.
4. Type two commands, each followed by Enter.- 1. [to disable SIP]: csrutil disable
2. [to mark Motu's dev ID "always trusted"]: /usr/sbin/spctl kext-consent add KRCLLMGZ2D
6. Open Terminal
7. Paste this exact line into Terminal: sudo kextload /Library/Extensions/Motu\ MIDI\ Driver.kext
8. Enter your password, press Enter
9. Go to System Preferences --> Security --> enter your password --> click the "Allow" button.
10. Restart normally
11. Confirm that you can see and use your MIDI device
12. Restart into Recovery Mode and open Terminal (#2-3 above)
13. Type: csrutil enable
14. Press enter --> restart your computer normally. - 1. [to disable SIP]: csrutil disable