Importing templates one by one is time consuming. You can import all the templates in a directory at once. Elementor CLI library import-dir command will import all the template JSON files using the command line.
wp elementor library import-dir <dir-path><dir-path>
(Required) A path to the directory.
wp elementor library import-dir path/to/custom-templates/This command will import to the library all template JSON files in the path/to/custom-templates/ directory.