My friend has recently acquired a Dell OptiPlex 780 mini tower computer running Windows 11 Pro OS.

When trying to install Windows security updates I get this message, "Your version of Windows has reached the end of service".  I thought any version of Windows 11 should allow security updates but that doesn't seem to be the case.

I have done some research online and it seems all I need to do is change from legacy to UEFI in the boot list option within the BIOS settings.  This will then also allow 'Secure Boot State' which is currently unsupported. 

However, when entering BIOS (A15) there is no 'Boot List' option to enable me to do this.  All I can do is select the order of boot devices.

It seems ironic that all the hoo-hah of "you should move from Windows 10 to Windows 11 now" still doesn't necessarily fix the issue of installing security updates.  

I tried upgrading to Windows 11 24H2 but it wouldn't run, as Secure Boot was not found in BIOS as explained earlier.

Please can anyone help with this?

Thank you,

Dave S.