Additional CSS missing in Twenty-Twenty-Two

The full site editor is replacing the customizer but you can still access it at /wp-admin/customize.php.

Justin Tadlock covers that whole question and more in this article. Part of the answer: the Customizer isn’t gone, just not linked to. So you can just “hack” your way to it at /wp-admin/customize.php. And with that, all is restored.

– https://wpshout.com/links/you-might-miss-the-customizer-in-wp-5-9/

Further reading:

• https://wptavern.com/customizer-will-disappear-for-some-block-theme-users-with-wordpress-5-9
• https://fullsiteediting.com/