Hi Florian,
Thanks for contacting Syncfusion support.
At present there is no support to add multiple tasks in one row. For this we have already logged a feature request regarding this.
A support incident has been created under your account to track the status of this requirement. Please log on to our support website to check for further updates.
Please let us know if you require further assistance on this.
Regards,
Jone sherine P S