I can't update the system

There's an available update (macOS catalina 10.15.4). I click the Update now button and the window to restart the computer opens. I click to restart and it restarts. I go to the same update menu, click Update now and the very same button appears yet again.

This is an endless loop (I've restarted my laptop about 7 times already trying different solutions) and I can't get over it and update the system.