USB is not displayed in the boot menu

[φιλα_δελφία]

Dear Steam Deck users!
I tried to boot Smokeless_UMFA from a USB stick I formated via KDE Partition Manager (I did exactly als CryoByte33 recommended in his video) unfortunately non of the three sticks I tested shows up in the boot menu at all. Has someone made the same experience and/or does know a fix?
Thank you very much!
phil

[Ferrox One]

Same problem