Dear Gkouk74,
First, my pleasure to assist you.
As per your description, I understand you want to SharePoint online Task List send Email Notifications to an owner at once per week for their overdue tasks and due task within the next 7 days,
As in SharePoint online task list, based on my test I checked there is no setting option to send Email notifications to the task owners once per week for overdue tasks and due within the next 7 days.
However, I think it will be possible through Microsoft Flow Power automate trigger and I search a lot to find a Microsoft Flow but unfortunately couldn't find related information. For Microsoft Flow Power automate trigger solution and to avoid any incorrect information from our side, we’ll suggest you post in Microsoft Power Automate Community for expert assistance. This is a specific channel related to issues with Microsoft Flow Power Automate.
Your understanding and patience will be highly appreciated. I hope that you are keeping safe and well!
Sincerely,
Waqas Muhammad