I have read through the history of posts similar to these on the site and sent the logs from 1.15.2 since 1.12 isn't supported. I get the same error either way and the connection logs from the server are attached. I have the exact same mods in the folder and forge is installed and shows as connecting.
message.txt
My friend created a server using a docker image for skyfactory 4.
https://hub.docker.com/r/filoozom/skyfactory4
When I try to join the server it gives me the error "this server has mods that require fml/forge to be installed on the client" I have forge installed on the client with the correct version being launched. I also have the mods in the mod folder that I pulled from the docker page he is using for the image.