If you plugin is active, the theme customiser throws a fatal error (regardless of which theme used), php error log (php 8.3):

Stack trace:
#0 /wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters(NULL, Array)
#1 /wp-includes/plugin.php(517): WP_Hook->do_action(Array)
#2 /wp-includes/class-wp-customize-manager.php(947): do_action('customize_regis...', Object(WP_Customize_Manager))
#3 /wp-includes/class-wp-hook.php(324): WP_Customize_Manager->wp_loaded('')
#4 /wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters(NULL, Array)
#5 /wp-includes/plugin.php(517): WP_Hook->do_action(Array)
#6 /wp-settings.php(726): do_action('wp_loaded')
#7 /wp-config.php(92): require_once('/home/htdocs/u3...')
#8 /wp-load.php(50): require_once('/home/htdocs/u3...')
#9 /wp-admin/admin.php(34): require_once('/home/htdocs/u3...')
#10 /wp-admin/customize.php(13): require_once('/home/htdocs/u3...')
#11 {main}
  thrown in /wp-includes/class-wp-hook.php on line 324
[23-Jan-2025 21:21:07 UTC] PHP Fatal error:  Uncaught TypeError: call_user_func_array(): Argument #1 ($callback) must be a valid callback, function "color_picker" not found or invalid function name in /wp-includes/class-wp-hook.php:324
Stack trace: