orsomannaro Hi
Kindly review for the following :
1) You may check with your hosting provider if they have some server-side caching enabled due to which modifications or changes might not reflect at times as I have replicated the same on local install with default joomla template as GPDR consent checkbox appears fine. Ref: Screenshot
2) To troubleshoot, You may try to assign default joomla template to see if it appears ?
3) Try to clear your browser cache for changes to reflect as I could see cache enabled in global configuration and having temporarily disabled the same for troubleshooting purposes as the site might store and reflect old webpages irrespective of changes or modifications being done at times due to same being enabled