I have just installed the latest Forge for Minecraft 1.16.1 and now receive a "Warning" message when I create a new world in Single Player Mode...message states, "Worlds using experimental settings are not supported".
Following this, the world sometimes generates but just as often crashes the game. I am familiar with a host of Forge issues but I do not recall seeing this one before on world generation. Is it normal and I just need to cross my fingers or is it related to one of the 66 mods I have in my pack?