how to stop upgrade notification to Catalia or BigSur on Mojave

By replacing files of Mojave 10.14.6 (18G5033)

Replacing the SoftwareUpdate.framework file in "/ System / Library / PrivateFrameworks /" with that of 18G4032 corrects the appearance of the Catalina and  BigSur update notification.

How to do:

1), #Make a backup of SoftwareUpdate.framework existing in / System / Library / PrivateFrameworks /

sudo cp -R /System/Library/PrivateFrameworks/SoftwareUpdate.framework /System/Library/PrivateFrameworks/SoftwareUpdate.framework.backup

2), #Copy the file SoftwareUpdate.framework (uncompressed) in the folder / System / Library / PrivateFrameworks / (overwrite the existing one, DO NOT MERGE)

3), #then with terminal:

sudo chmod -R 755 /System/Library/PrivateFrameworks/SoftwareUpdate.framework;

sudo chown -R 0: 0 /System/Library/PrivateFrameworks/SoftwareUpdate.framework

##. How to disable SIP on MAC in command line:

From the Terminal, run the following commands:

sudo nvram "recovery-boot-mode=unused"

sudo reboot recovery

From the menu bar click Utilities > Terminal

Run csrutil disable from the terminal, followed by reboot

Once your VM has rebooted normally you can verify that SIP was disabled by opening a terminal and running csrutil status

after done, run: nvram -d recovery-boot-mode , back to the normal boot mode.