OK, this makes sense. Then please test this instead.
João
diff --git a/lisp/progmodes/eglot.el b/lisp/progmodes/eglot.el
index e2478f2dde3..c353ab6fce0 100644
--- a/lisp/progmodes/eglot.el
+++ b/lisp/progmodes/eglot.el
@@ -3348,9 +3348,11 @@ eglot--imenu-DocumentSymbol
(mapcar (lambda (c) (apply #'dfs
c)) children))))))
(mapcar (lambda (s) (apply #'dfs s)) res)))
-(defun eglot-imenu ()
+(cl-defun eglot-imenu ()
"Eglot's `imenu-create-index-function'.
Returns a list as described in docstring of
`imenu--index-alist'."
+ (unless (eglot--server-capable :textDocument/documentSymbol)
+ (cl-return-from eglot-imenu))
(let* ((res (eglot--request (eglot--current-server-or-lose)
:textDocument/documentSymbol
`(:textDocument