LSP server unbound module Thread error

The application compiles correctly but there is an error with the functionality of the editor,

my .ml file contains

open Thread;;
let t1=Thread.create myfun () in

my .merlin file contains

PKG unix threads

The neovim editor returns as error:

ocamllsp: Unbound module Thread

An error between “singular and plural ?”

For beginners, it’s recommended to use dune (which may autogenerate .merlin files). Moreover, new versions of merlin do not require to generate .merlin files, so it’s highly likely that your .merlin file is simply ignored.

Using dune the lsp worked fine.

How would this be solved without using dune? Are .merlin files ignored by ocamllsp?