Hi @MTG ,
Do you mean to synchronize the items in the two lists?
The item in list A is created/deleted/modified, and the corresponding item in List B is also created/deleted/modified.
If this is the case, we need to set a reference field to identify the corresponding items. I suggest adding an ItemID(Number type) field in list B to record the ID of the item in List A.
Please refer to the screenshot below to configure Flow:

Note: The Dynamic content in Create item is all from When an item is created or modified.
The ID configured in Update item is from Get items, the ItemID field is not need to configured, and the rest of the field configuration Dynamic content is all from When an item is created or modified.
Hope it helps.
Best Regards,