@Alessandro-Floris the link you're following is for the Omega 1, which is based on OpenWRT. The Omega 2 makes use of LEDE, which is a branch/fork of OpenWRT. Ergo, you need to use the LEDE toolchain. Searching this forum should reveal some light on the matter.

I remember users like @Kit-Bishop and @WereCatf making posts about it.