I got a bit further: It seems the ELESION app is just a re-branded Tuya app. You need to sign up for a Tuya developper account at https://eu.iot.tuya.com to do so, you can’t use the ELESION app (the QR-code pairing always fails). Sou you need to remove all devices there and add them to the Tuya app. they will then become available in the Tuya integration once you paired the Tuya cloud with HomeAssistant.
However, I can’t control any of the devices I now see in HA. Same issue as described here.