Why does this dplyr::select(where( statement not work (must return a boolean)?

Question

I am using this select statement

mtcars %>% 
  select(
    where(
      function(x) is.numeric(x) | mean(x) > 10
    )
  )

However, I get the error saying:

Error in `dplyr::select()`:
! `where()` must be used with functions that return `TRUE` or `FALSE`.
Backtrace:
  1. mtcars %>% ...
  3. dplyr:::select.data.frame(...)
  6. tidyselect::eval_select(expr(c(...)), .data)
  7. tidyselect:::eval_select_impl(...)
 16. tidyselect:::vars_select_eval(...)
     ...
 19. tidyselect:::reduce_sels(node, data_mask, context_mask, init = init)
 20. tidyselect:::walk_data_tree(new, data_mask, context_mask)
 21. tidyselect:::as_indices_sel_impl(...)
 23. purrr::map_lgl(data, predicate)
 24. tidyselect .f(.x[[i]], ...)

But isn`t the function returning a boolean?