Not compatible with WordPress 6.7+ and solution

In printful-shipping.php, line 79, the Printful_Shipping singleton is initialized, which depends on translations. This method is hooked onto plugins_loaded, which is too early for translations.

It’s possible the entire method can be hooked onto init instead, or it’s possible it needs to be split out into two methods with different hooks. Worst-case scenario, init is too late for some of the other work done in the Printful_Shipping class, but that seems unlikely.