Since WordPress released the 5.9 version to the public on January 25, 2022. WordPress introduced a new default theme, Twenty Twenty-Two. Twenty Twenty-Two is the block theme that allows you to design the entire site, including the header, footer, and everything in between, with blocks using the Site Editor. In previous versions, you could only edit partially, not a Full Site Editing (FSE).
Block themes have the main benefit that no code is required. Well, it sounds good. But wait, this theme is not perfect. In the block themes, you can’t find the Theme Customizer anymore, which it’s a feature only available if you’re using the classic themes.
Many WordPress users, including us, can’t move on from the Theme Customizer feature. With Theme Customizer, you can change your Site Title and Tagline, add classic widgets to a sidebar or footer, create menus, edit your homepage settings, and last but not least, you can add the CSS code in the Additional CSS block.
This article will show you how to enable the customizer when you’re using a block theme in WordPress.

How to Enable Theme Customizer on Block Theme in WordPress
Before starting the tutorial, we would like to inform you that you don’t need to follow the tutorial when you’ve activated a block theme on your WordPress and using Yoast. Activating Yoast will automatically enable the theme customizer, which will display on the Appearance menu.

Alright, let’s start the tutorial!
Go to your WordPress dashboard, then navigate to Tools -> Theme File Editor.

Once you click the Theme File Editor menu, please navigate to the Theme Files panel; you will find some files. Select functions.php and click on it.

Next, we will add the simple PHP snippet into the functions.php file to enable the theme customizer on the WordPress block theme.
Note: If you are afraid of breaking your site after adding the new function to the functions.php file, you can use the Code Snippets plugin to add a custom function in WordPress. Read here to learn more.
Afterward, copy the PHP snippet below and paste it to the end of the functions.php file content.
add_action( 'customize_register', '__return_true' );
Once you paste the PHP snippet to the functions.php file, don’t forget to apply it by clicking the Update File button.

That’s it. Go back to your WordPress dashboard and go to Appearance, and now your theme customizer is enabled on your block theme and ready to use.

The Bottom Line
Until this article was made, there were 200+ block themes available on the WordPress theme directory that you could download for free. But, compared with classic themes, they have 10.000+ themes available there. So, the conclusion is that classic themes are still the most widely used option.
As we know, block themes are fully compatible with Full Site Editing (FSE), but the problem is that it’s still in the beta version. So, we highly recommend using WordPress page builder plugins if you want a better experience in building and designing a website, such as Elementor, Divi, Brizy, etc.