Can't boot my LUKS/LVM Debian 10 on my UEFI-based Lenovo ThinkPad X390 (dual-boot with Windows)

[<l0f4r0@tuta.io>]

Hi everyone,

I installed some days ago Debian 10 with LVM inside LUKS and specific partioning (4 logical volumes for /, /home, /var and swap) on my UEFI-based Lenovo ThinkPad X390 in dual-boot configuration with Windows 10 (which came preinstalled on this brand new laptop).

Everything went well except I can't boot on my Debian, I don't even see Grub. Windows is launched automatically instead.
My only solution is to launch a rEFInd USB key, boot on it and select either "Boot EFI\Boot\grubx64.efi from SYSTEM" or "Boot EFI\debian\grubx64.efi from SYSTEM" (among 6 options) in order to launch my Debian. It's not very handy but it seems to indicate I'm not very far from the solution because everything works fine after that (it proves that my Linux is well installed)...

I've created a thread on LinuxQuestions at https://www.linuxquestions.org/questions/debian-26/no-grub-to-launch-my-new-debian-10-with-luks-and-lvm-uefi-4175666362/.
There are many useful information/details about my situation at this URL and you will see I've already tried a few operations (including some with efibootmgr), with no avail so far... 

I would be very grateful if some people could help me regarding this matter :)

_NB:_ Please tell me if this is not the most appropriate place to discuss all of this (I've already posted my issue on LQ and debian-user ML and still don't know how to resolve this). Maybe this ML is more about development but sometimes development and issues are related ;)

Thank you in advance & Best regards,
l0f4r0