I turned on the opt to install the developer beta on my 15 Pro Max. It downloaded 18.1 but none of the newer features are available such as the apple intelligence and RCS support. I am assuming that I don’t have the newest version of the developer beta, but it isn’t being offered to me to download. Any help with this would be most appreciated.
iOS 18.1 is the only version that will download
Check which version you have installed in Settings > General > About, then compare it with the latest version Apple released.
RCS, I believe, needs to be supported by your carrier.