Suggest after installing kde, install efibootmgr package and do "bootctl install"
Note many people here have a 'linux boot manager' or "Systemd Boot Manager" in their efibootmgr entries, meaning they have done 'bootclt install' as well.
It will save a lot of hassles later on as you had and easier to fix as well if you have problems.
clr-bootmgr is good to 'unify' uefi and bios-legacy boots (grub or systemd-boot) but for uefi, advisable to have this explicitly installed.