That’s strange. The signatures of LanguageServer.jl may very well have changed, but the eglot package should have things pinned to a working version of the language server. Could you try instantiating the environment in the REPL and see if it works without modifying the arguments? Maybe using LanguageServer is picking up the wrong version despite the Manifest.toml.
In general, for troubleshooting, please post the output of the eglot stderr buffer. It’s much more useful for me to tell what’s going on.