This is a subject I see talked about online time and time again. It must get frustrating as hell, which is why you are probably here having google searched to get an answer. It seems some have zero issues, others have major issues after updating. Thankfully someone on Facebook has contacted UAD and got an answer as of the 4th of January 2019. So if you are one of the thousands of people wondering when the driver for the Apollo units is coming out for IOS Mojave here is your answer.
Max (Universal Audio)
Jan 4, 6:37 AM PST
Thanks for contacting us.
We are still working on fully qualifying Mojave for UAD software and hope to release a new UAD version with Mojave support as soon as possible. However we do not have an exact release date yet.
If you are getting the driver not installed correctly error then this usually means that you need to allow the software in the MacOS Security and Privacy settings.
Please see macOS 10.13 High Sierra Compatibility Info. This also applies for Mojave.
Since the option to allow the software is only available for the first 30 minutes after the installation you will probably have to uninstall/ reinstall the UAD software for the Allow button to reappear.
-> (Mac) Apollo Uninstall / Reinstall Procedure
Also see macOS 10.14 Mojave Compatibility Info
Let me know if this helps