Uncaught TypeErrors when using Crop Thumbnails locally

I recently migrated a project to my local machine and for some reason, I keep getting errors when using the Crop Thumbnails plugin.

When I run the plugin quick test, I get Failure processing the test - have a look on your server logs., WP debug log shows

PHP Fatal error:  Uncaught TypeError: join(): Argument #2 ($array) must be of type ?array, string given in C:\xampp\htdocs\xxx\wp-content\plugins\crop-thumbnails\functions\settingsscreen.php:374
Stack trace:
#0 C:\xampp\htdocs\xxx\wp-content\plugins\crop-thumbnails\functions\settingsscreen.php(374): join(Array, '<br />')
#1 C:\xampp\htdocs\xxx\wp-includes\class-wp-hook.php(292): CropThumbnailsSettingsScreen->ajax_callback_admin_quicktest('')
#2 C:\xampp\htdocs\xxx\wp-includes\class-wp-hook.php(316): WP_Hook->apply_filters('', Array)
#3 C:\xampp\htdocs\xxx\wp-includes\plugin.php(484): WP_Hook->do_action(Array)
#4 C:\xampp\htdocs\xxx\wp-admin\admin-ajax.php(187): do_action('wp_ajax_ctpplug...')
#5 {main}
  thrown in C:\xampp\htdocs\xxx\wp-content\plugins\crop-thumbnails\functions\settingsscreen.php on line 374

When I try cropping an image in the media section, I get

PHP Fatal error:  Uncaught TypeError: copy(): Argument #1 ($from) must be of type string, WP_Error given in C:\xampp\htdocs\xxx\wp-content\plugins\crop-thumbnails\functions\save.php:102
Stack trace:
#0 C:\xampp\htdocs\xxx\wp-content\plugins\crop-thumbnails\functions\save.php(102): copy(Object(WP_Error), 'C:\\xampp\\htdocs...')
#1 C:\xampp\htdocs\xxx\wp-content\plugins\crop-thumbnails\functions\save.php(247): CptSaveThumbnail::saveThumbnail()
#2 C:\xampp\htdocs\xxx\wp-includes\class-wp-hook.php(292): CptSaveThumbnail::saveThumbnailAjaxWrap('')
#3 C:\xampp\htdocs\xxx\wp-includes\class-wp-hook.php(316): WP_Hook->apply_filters('', Array)
#4 C:\xampp\htdocs\xxx\wp-includes\plugin.php(484): WP_Hook->do_action(Array)
#5 C:\xampp\htdocs\xxx\wp-admin\admin-ajax.php(187): do_action('wp_ajax_cptSave...')
#6 {main}
  thrown in C:\xampp\htdocs\xxx\wp-content\plugins\crop-thumbnails\functions\save.php on line 102

I’m running the same WP and plugin versions on prod and local, PHP versions are 7.3.27 on prod and 7.4.3 on local via apache. Do you have any idea, what to do to make it work on both environments?