The CSM option to only show UEFI boot devices does seem a bit buggy though. Sometimes if i have reset all bios settings i can have a big list of bootable devices, but they are all non UEFI except one UEFI for Windows and one UEFI for Ubuntu.
To solve it i have to unplug both the windows and ubuntu drives, boot the computer (with no boot drive/partition connected it will go straight into bios), shut down the computer, reconnect the drives and then it will look better with only the UEFI boot devices showing.
Anyway, hope you get it to work.