No Grub to launch my new Debian 10 with LUKS&LVM (UEFI)

[<l0f4r0@tuta.io>]

Hi everyone,

I installed some days ago Debian 10 with LVM inside LUKS and specific formatting (4 logical volumes for /, /home, /var and swap) on my 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 easily 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/
You should get any useful information/details about my situation at this URL and you will see I've already tried a few operations, with no avail so far... 
As I don't receive any new suggestion from the LQ community during the last few days, I've decided to write to this ML.

I would be very grateful if some people could help me regarding this matter :)
Thank you in advance & Best regards,
l0f4r0