WordPress 5.5 will contain several changes to existing features that will directly impact themes. This theme specific field guide details a few changes and also links several that were previously published separately.
Theme compatibility checks
In WordPress 5.4, support was added to the style.css file for the RequiresWP (Requires at least) and RequiresPHP (Requires PHP) file headers (see #44592). These headers allow theme authors to define the minimum versions of WordPress and PHP required to reliably run their themes. Though support was added for these headers, they were not yet used in Core.
In 5.5, the values provided by these