Support for inlay hints in go files about lsp-mode HOT 1 OPEN

This is what I use in my init.el to get inlay hints in go files, maybe it could be of help to what you're trying to do

   (lsp-register-custom-settings
    '(("gopls.hints" ((assignVariableTypes . t)
                      (compositeLiteralFields . t)
                      (compositeLiteralTypes . t)
                      (constantValues . t)
                      (functionTypeParameters . t)
                      (parameterNames . t)
                      (rangeVariableTypes . t)))))

Also fyi currently there is a bug in lsp-mode where if you have this set in your early-init.el

  (setenv "LSP_USE_PLISTS" "true")
  (setq lsp-use-plists t)

then despite registering the settings with lsp-register-custom-settings you will still get the error message that inlay hints are not supported by the connected server (See #4325). So that also might possibly be the cause of the error

from lsp-mode.