Unable to Update to 10.15.6 from 10.15.5

[$tealth]

HI, 

I have MAC BOOK AIR Dec 2017. I have Quad OS installed on the computer on the same Harddisk 

1. MACOS X 10.13.6 

2. MACOSX 10.14.6 

3. MACOSX 10.15.5 - Update unsuccessful to 10.15.6 

4. MACOS 11 Big Sur 

 

I have installed all these OS on the same Harddrive. When I try to update via the Update MACOSX 10.5.6  option the update continuous for some time computer restarts and update does not take place. 

I have even tried using the combo pack to update and SMC Reset and NV Ram Reset I have tried. Does anybody have any other option to update combo pack 

 

Appreciate your help 

Thanking you 

$tealth 

[Ethan Jarvis]

 

I would like to suggest you try to Boot into Safe Mode and then download & install the macOS Catalina 10.15.6 Combo Update.