I copied the link and executed this command on my router: opkg install https://downloads.openwrt.org/releases/22.03.2/targets/lantiq/xrx200/packages/libc_1.2.3-4_mips_24kc.ipk but without success since it gives me an error.
Is what I'm doing correct? I need to install every dependency for the packages that I need?
I don't think I'm able to get this working. Now I would like to revert to the original firmware, maybe I'll be able to do that. Or else I'll have a paperweight
You compiled an image yourself and fail to add a package to it!? Did you ever read my comment and/or try what I suggested (include LuCI directly in the build)?
@armSeb states select packages, so you need to find if Luci is available in the @armSeb fork.
So I would go back through compiling or let us know what you want to do in Luci and I'm happy to give a quick terminal guide to UCI to do the same job as Luci.
If this is a problem I can download and compile @armSeb fork, and build this for you if required though I think you are more than capable of this.