This instruction page for the Netgear R6900v2 had me installing "snapshot images" that do not contain LuCi and not "stable" images which do.
As a result, I thought I had bricked the router because I couldn't bring up LuCi. I struggled for several hours with it before I figured out what happened. I resolved the problem by SCP the proper image to the router and then SSH to command the upgrade.
I do see the proper stable images toward the bottom under "Hardware" but I find this misleading especially since the "OEM easy installation" directed me to install the image "shown above.".
I suggest that the "stable" image Including LuCi should appear in the "Installation" section.
Note that all documentation is produced by volunteers and only updated when someone gets round to it.
Also, OpenWrt is not a product of a large Corporation. It is intended for both "enthusiasts" and "developers" to use as they see fit.
You seem to be an enthusiast, perhaps at the early stages of learning and as such have become somewhat frustrated by the documentation. Making suggestions, sharing your experiences and asking for help are good ideas, but please first read any of the OpenWrt documentation fully, baring in mind my comments.
In this particular case the document clearly warns:
Fix Me! These are generic instructions. Update with your router's specifics.
and
Supported Current Release 24.10.5
So read carefully, use common sense, and learn from the experience. Don't just blindly follow a paragraph without thinking, read around it, ask on this forum, then, fairly soon, when you fully understand the issues, you can contribute and rewrite the documentation yourself.