You need to disable Remote Play under Relive Game Streaming. Once this is disabled, Eyefinity tab will reappear again.
See if you have,by any chance, Remote Play enabled under Relive. If you do, disable it and restart Radeon Settings. Eyefinity Tab should appear now.
If the above doesn't work then you have another problem.
it is no longer called Remote play and relive.
try going to SETTINGS, then go to DEVICES TAB and disable "AMD Link Server".
after that check on the DISPLAY tab and you'll definitely find "Eyefinity" at the bottom
I tried it myself. hopefully, this works for you too