WordPress Customize Erro

Try disabling all plugins and switching to a default WP theme.

This is caused by a default memory limit on your server. There are a number of ways to increase the memory limit (but it will depend upon your server).

One way to do this is to add the line
define(‘WP_MEMORY_LIMIT’, ‘128M’); in your wp-config.php

Make sure, though, before you do this, that you have a backup of the file. Any errors including typos in your wp-config.php will crash the whole site.

See here for more details: https://www.wpbeginner.com/wp-tutorials/fix-wordpress-memory-exhausted-error-increase-php-memory/