TL;DR: Windows doesn't start from GRUB with secure boot disabled after installing Manjaro
recently I've installed Manjaro Linux on a computer which had Windows pre-installed. My goal was to be able to dual-boot Manjaro and Windows. The bespoken computer (Lenovo ThinkPad) is equipped with UEFI and only one hard drive.
Before installing Manjaro, I've created a new unformatted partition in Windows and disabled the UEFI secure boot option. The installation itself hadn't run into any problem, it works fine for now.
Now, in GRUB I see menu entries for Manjaro Linux (which works fine) and Windows 10 (on /dev/sda2). When selecting Windows, the screen turns black for a while and then the computer restarts and GRUB shows up again. When selecting to start "Windows Boot Manager" from the UEFI startup selection (after pressing F12 key) the screen turns black for the fraction of a second and startup selection shows up again.
I've tried re-activating secure boot in UEFI configuration again. Windows now starts as it should, but it's not possible to enter GRUB anymore until I disable secure boot once again.
Since I'm fairly new to this topic, I really don't know how to go on.
I therefore appreciate your help.
Thank you in advance!