Thank’s!
I see, I thought the R version was on 12L
It would be useful to show the android version next to the letter version of /e/ 
For now, I have unlocked the bootloader, then I tried to flash /e/ recovery, the flash have worked, but when I try to boot onto recovery mode, the phone boot as normal and don’t show me the recovery menu.
I searched the forum, and I’m a bit submerged by the differents informations. I don’t know if I need to root the phone, or downgrade the firmware to install a custom recovery.
Right now, my config is :
Model: SM-G975F/DS
Android version: 12
CP: G975FXXUFHVG4
Can anyone help me? 
UPDATE : I found this post: Installing /e/OS on a Samsung Galaxy S10+ with latest Android 12 revision - #4 by Geron and start to try the solution mentioned