Problem solved, I think the wiki instructions for installation should be completed with one optional step as I describe here.
Wiki page for /e/ installation on Xiamo Rednote 5.
Source for the fix.
On the Installing a custom recovery part, at 5 is recommended to do :
fastboot flash recovery twrp-x.x.x-x-whyred.img
I’d recommend the following :
(optional) If 5 failed because of anti-rollback check, download the ARB bypasser here. Extract the content and use it for :
fastboot flash antirbpass FILE.img
fastboot flash recovery twrp-x.x.x-x-whyred.img
There is a way (that I can’t find back) to avoid this and still install /e/ but TWRP won’t be installed and, for example, make any update impossible as it recquires a compatible recovery.
I didn’t dare post this directly on the GitLab as an issue, I hope I did right and, more, I hope this will help.