Welcome to the forum. As @Martin_Webster mentioned, we can only support Roon when Core, Remotes and Endpoints are on the same subnet. Since you have multiple subnets set up, you are in #tinkering territory, and I have moved your post over to this sub-section.
There are a few threads on the forum of users who managed to get Roon working on a non-flat network if you search around, but as I mentioned, these are not officially supported and you’ll have to try and see what works yourself.
Roon uses multicast for endpoint device discovery, and remote to Core connections, so a few have mentioned the need for an mDNS reflector: