php 8.2

It’s addressed in the upcoming 3.5.0 version.

In the meantime (and I don’t generally recommend making changes directly to the plugin, but in this instance, it wouldn’t matter), if for some reason you run a production site with PHP warnings and notices turned on (which you shouldn’t do, but that’s a different discussion), then add the declaration to the list of vars at the beginning of /includes/class-wp-members.php (the main object class):

public $reg_form_is_showing;