A new version of the popular Seamless Co-op modification has been released for Elden Ring, adding full-fledged co-op. Now it supports all the content from the Shadow of the Erdtree expansion.
The original version of Elden Ring allows summoning allies only in certain locations, but Seamless Co-op removes this restriction. With its help, you can play through the entire game in a team of up to six people.
The mod does not allow the game to connect to FromSoftware's servers, so you don't have to worry about anti-cheat. The author does not recommend running Seamless Co-op with other modifications.
You can download the co-op mode here.