Info file
In
/modules/k4.info.yml
name: k4
description: k4 module.
package: AAA
type: module
core_version_requirement: ^8 || ^9
Routing file
In
/modules/k4.routing.yml
k4.listprojects:
path: '/k4/list_projects'
defaults:
_controller: '\Drupal\k4\Controller\k4ListProjectController::app'
_title: ''
requirements:
_permission: 'access content'
libraries file
In
/modules/k4.libraries.yml 
