chenge to sierra

Downgrading from Mojave to Sierra will require that you backup your Mac, erase and reformat the startup drive, reinstall the earlier OS and then restore your data from the backup. It is not a trivial task.

As posted by Latranner above, Mojave is more current, more secure and still has some support from Apple. A better option would be to eliminate whatever problem might be prompting you to downgrade, and then continue to use Mojave or even to upgrade to Catalina.

I'l ask the same question, why do you believe you need to downgrade?

Hello again. Is it possible to get updated software for your instrument? It looks like Native Instruments offers a device updater that you could use to update the firmware of your device, potentially enabling it to support newer versions of macOS. macOS Sierra is very old at this point and if you downgrade to it to use your Native Instruments controller you may struggle to run other software.

Hello. Is there a reason that you want to downgrade from macOS Mojave to macOS Sierra? MacOS Mojave has better software support than macOS Sierra. As all Macs that support Mojave also support Catalina, you also can upgrade to macOS Catalina (10.15) or newer, depending on the age of your Mac.

Hello. You could also purchase a newer device from Native Instruments that has support for more recent versions of macOS, but I understand that this can be a costly undertaking.

Ultimately, the decision to downgrade to Sierra is up to you as the owner of the MacBook Pro in question. Please just be aware that you may encounter additional compatibility issues after doing this and remember that Sierra is no longer supported by Apple. Software that you are running on Mojave may no longer work on Sierra.

Another option would be to install macOS Sierra on an external USB SSD drive and use that as a startup disk when you must use the Native Instruments gear. The newer OS will remain intact and usable on MBPs internal drive. It'll be easier to setup and execute than will be wiping the drive and all that is required for that option.