macOS reboots after booting from update installer

When I boot the macOS installer (I'm trying to update) the loading screen appears and after around 5 seconds, the screen turns black and reboots. Any ideas?

^{SMBIOS: iMac20,1 Intel Core i5-10500 @ 3.10 GHz
CPU: 5800X3D MOBO: B550M DS3H CSM: Disabled}