Nextcloud Mail App Mailvelope Integration

We use Nextcloud with the Mail App. Additional we plan to use Mailvelope.

Could you inform us, how we can switch to API mode to use the Mailvelope integration?

It is mentioned in this post:

Can you provide us a tutorial?

Thanks

Install the Mailvelope extension. Open its settings. Then when you configure your domain there is a switch for “API”. Switch it ON.