AlmaLinux 8.6 : Automatically shutdown guest machines on virtual host

I have setup an AlmaLinux 8.6 server as a virtualisation host. I want to know what the default behavior is when you restart the virtual host.

Also how would I customise the server to suspend certain guests on reboot/shutdown or shutdown certain guests on reboot/shutdown?

that’s what libvirtd and libvirt-guests is for - starts guests configured to autostart on boot, and suspends them on shutdown.