Use custom content entity theme suggestions in own module?
To make a theme suggestion work in the module folder you need an additional theme hook:
function offer_theme($existing, $type, $theme, $path) {
  return [
    'offer' =&gt; [
      'render element' =&gt; 'elements',
    ],
    'offer__full' =&gt; [
      'base hook' =&gt; 'offer',
    ],
  ];
}