Calling (require ...) on a MELPA installed package gives FlyCheck error "Cannot open load file" - emacs

Question

I want to require some packages installed through MELPA so that i can access their variables and functions without getting "free variable" or "undefined function" warnings.
However, when I try to load a package it isn't found by Flycheck and i get a "Cannot open load file" error. It seems that the bytecode compiler doesn't read into the directory with the files installed by MELPA, but I don't know how to solve this.
I'm using Emacs 26.3 with Purcell's config that includes Flymake-Flycheck. This snippet covers the relevant parts of the init-elpa.el custom files where you can see the at the end that even if I install and then (require ...) a package it still is marked with an error by Flycheck.
;;; init-elpa.el --- Settings and helpers for package.el -*- lexical-binding: t -*-
(require 'package)
(require 'cl-lib)
;;; Install into separate package dirs for each Emacs version, to prevent bytecode incompatibility
(setq package-user-dir
(expand-file-name (format "elpa-%s.%s" emacs-major-version emacs-minor-version)
user-emacs-directory))
;;; Standard package repositories
(add-to-list 'package-archives '( "melpa" . "https://melpa.org/packages/") t)
(defun require-package (package &optional min-version no-refresh)
"Install given PACKAGE, optionally requiring MIN-VERSION.
If NO-REFRESH is non-nil, the available package lists will not be
re-downloaded in order to locate PACKAGE."
...)
(defun maybe-require-package (package &optional min-version no-refresh)
"Try to install PACKAGE, and return non-nil if successful.
In the event of failure, return nil and print a warning message.
Optionally require MIN-VERSION. If NO-REFRESH is non-nil, the
available package lists will not be re-downloaded in order to
locate PACKAGE."
...)
;;; Fire up package.el
(setq package-enable-at-startup nil)
(package-initialize)
(defvar sanityinc/required-packages nil)
(defun sanityinc/note-selected-package (oldfun package &rest args)
"If OLDFUN reports PACKAGE was successfully installed, note that fact.
The package name is noted by adding it to
`sanityinc/required-packages'. This function is used as an
advice for `require-package', to which ARGS are passed."
...)
(advice-add 'require-package :around 'sanityinc/note-selected-package)
(when (fboundp 'package--save-selected-packages)
(require-package 'seq)
(add-hook 'after-init-hook
(lambda ()
(package--save-selected-packages
(seq-uniq (append sanityinc/required-packages package-selected-packages))))))
;; READ HERE: now i try to install and require some packages.
(require-package 'fullframe)
(require-package 'evil)
(require 'fullframe) ;; Flycheck gives an ERROR: cannot open load file, files or directory does not exist
(require 'evil) ;; same as above
(require 'python) ;;this gives no error, since it's built-in i guess.
(provide 'init-elpa)
;;; init-elpa.el ends here
You can see that (package-initialize) is called so the load-path should be set. Also, I have flycheck-emacs-lisp-load-path set to 'inherit, which should mean that the bytecode compiler reads the same dirs as a normal emacs instance.
What should I do in order to make the bytecode compiler recognize my ELPA directory?

Answer 1

Check out flycheck-emacs-lisp-load-path variable
flycheck-emacs-lisp-load-path is a variable defined in ‘flycheck.el’.
... When set to ‘inherit’, use the ‘load-path’ of the current Emacs
session during syntax checking.
E.g you could do:
(use-package flycheck
:diminish ""
:custom
(flycheck-emacs-lisp-load-path 'inherit)
...