Ok, so I kept on trying to find a solution myself.
I finally got it working, I will try to describe in detail how I did it. But first of, after installing 18.2.1 I went into the AMD folder and noticed that there was no CCC-Slim installed (I have no reason why since the "try advanced settings" in the eyefinity menu trigger the CCC-Slim application)
Any way I resolved it by going into the 18.2.1 folder (C:\AMD\Win10-64Bit-Radeon-Software-Adrenalin-Edition-18.2.1-Feb7) opened "Packages/Apps/CN/CCCSlim/Core-Static-Net4 (Scroll all the way down and you'll find a "ccc-slim.exe" file click and install it. After you've done that just restart your PC just in case. Now after restarting check if it's working now it did for me and it saved my day
Raw location for installing ccc-slim:
To find the location to manually open CCC-Slim:
C:\Program Files (x86)\AMD\CNext\CCCSlim
Hope this is helpful for those not being able to find a solution.
So I'm having the same issue as you were, however this hasn't fixed it. Only .exe in the folder is a MOM.InstallProxy.
Still cannot get advanced settings to show up.
You sure you're looking into the right folder?
It's not the installed folder you need to be looking at, its the unpacked driver folder which in my case is located C:\AMD\Win10-64Bit-Radeon-Software-Adrenalin-Edition-18.2.1-Feb7 in this folder there is the location I described above.
If you look into this location: C:\Program Files (x86)\AMD\CNext\CCCSlim you are looking into the wrong location where indeed will be this MOM.installproxy alone.
ps. in this example I use the 18.2.1 drivers but I reckon its the same for the newer 18.3.3 as well. Since it worked for the original title 18.3.1 as well.