Update

I assume you're clicking on Update Now in System Preferences > Software Update, as described here: How to update the software on your Mac.

Does the Software Update window say that the macOS 10.15.5 update is available? What does it do after clicking Update Now?

linde23 Said:

“Update My MacOS Catalina won't update from 10.15.4 to 10.15.5 even though I have enough space on my laptop. I've tried it several times already. What else could I try?”

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A Couple of Thoughts:

• Reset the SMC and your NVRAM:

Sometimes when changes are made to the system(i.e. updates), system configurations (i.e. for Keyboard) become manipulated, technically. So, reset the SMC and NVRAM. Your hard drive may not be being read promptly, so resetting these, all of the ports would be configured to how they should be.

• Create a New Administrator User:

See if this works when you create a new Administrator User. If it works, then it is obviously something misconfigured in the current user.

Forget System Preferences> Software Update.

Click on this link,

https://support.apple.com/kb/DL2040?viewlocale=en_US&locale=en_US

Once it has downloaded, double-click to install.

Before updating make a full back up of your Mac.

Connect your mac to your router via cable rather than rely on WiFi.

Do not use your mac while it is downloading

and do not use any other devices that share the same internet connection.