Hi @Anonymous,
Thanks for updating.
It seems that you are trying to update the ID of each list to each other.
In your last action Update Personal item, please make sure you are using the correct dynamic content ID for the Id field.
I have made the following flow for testing. In my scenario, I am trying to update Id of List A to column ListAId in List B, and update Id of List B to column ListBId in List A.
It is configured likes below.
Action Get items will get items from List B, a Filter query is used to filter out the item has a common value with the new item in list A.
As I am going to update list A using dynamic content from previous action, an apply to each is added automatically, and make sure select the correct dynamic content ID from the action Get item.
Action Update item 2 will update List B, please make sure select the dynamic content ID for the Id field from the action Get items.
Image for your reference.




Best regards,
Mabel