macOS 10.15.5 update not installed despite 30gb disk space I have 30gb of free disk space on 250gb disk which should be more than enough

I cannot install 10.15.5 it just restart and still says I haven’t installed

Update

Just now it wasn't showing the purgeable but now it is after my successful update.
Update the xcode to the latest version (I had to try this twice)
Restart
Try again to update to 10.15.5


This time it worked