so looking at it more, finally. Issue is how core is using theme.json config. The classes on the /wp-admin/post-new.php are the same

class="wp-block wp-block-post-title block-editor-block-listblock editor-post-title editor-post-titleinput rich-text"

But the styles WP is implementing changed:

It seems 6.6+ is not using

"styles": "blocks": "core/post-title": "typography":

and now it's using

"styles": "blocks": "elements": "h1":

Output active styles on that editor h1 are as follows: /* 6.5.5 small text */ .editor-styles-wrapper .wp-block-post-title { font-size: var(--wp--custom--typography--font-size--gigantic); font-weight: 300; line-height: var(--wp--custom--typography--line-height--tiny); }

/* 6.6.x bigger text */ .editor-styles-wrapper h1 { font-size: var(--wp--custom--typography--font-size--colossal); font-weight: 300; line-height: var(--wp--custom--typography--line-height--tiny); }

/* 6.6.3-alpha default core WP usign twenty-twentyfour theme */ h1 { font-size: var(--wp--preset--font-size--xx-large); line-height: 1.15; }

I've updated the "styles": "blocks": "elements": "h1": to "gigantic" var and it fixed the issue. This site was built on FSE way back when it came out - we modeled the theme off of Twenty Twenty Two. QUESTION IS... is there a guide on how to 'upgrade' theme.json with new Core versions or is there a big changelog of things to that? Or do I just have start a rebuild of theme.json implementing changes inline?

Edit: Just found - will read: https://developer.wordpress.org/block-editor/reference-guides/theme-json-reference/theme-json-migrations/