Dear M L,
Good day!!
I understand your concern and to my knowledge, there is no direct feature in the Microsoft Lists or SharePoint Online to automate the duplication of row but there is one quick process, where you can simply copy the data of the raw and paste it, please follow the below steps:
Go to the List> Edit in grid view> Double-click and drag your mouse to select the data in the row> Add New item> Paste the data> Exit Grid view.
If either it doesn’t work how you are expecting or you are looking only automate process, then I suggest you to give a shot by posting your concern in the Microsoft Power Automate Community - Power Platform Community to get the detailed help from the experts.
Apologies for redirecting you to different community as the members in the category posted focus on the users with the SharePoint Online out of the box concerns and have limited knowledge on the customization of Power Automate flow, so to get the fast and better assistance, we have redirected you in the correct path.
Appreciate your patience and understanding. Have a great day!!
Best Regards,
Sophia