disable Internet on the PC being installed e.g., unplug its ethernet cable.
In BIOS (F2) disable secure boot Rufus thumb drive is not secure enough for Dell BIOS Windows 11 install still prompts for e.g. US keyboard, offers option to install on thumb drive..!!
After Windows 11 installation, (F2) re-enable secure boot
check Event Viewer Administrative Events for Warnings and Errors