“How can I use Power Automate flow to create a SharePoint list item including the information to which users is the Planner task assigned?”
Exporting Planner task assigned users to Excel file was already covered, but what about a SharePoint list? The problem is still the same – the output of the ‘List tasks’ action. If it returned assigned user email addresses, you could easily update them to the SharePoint item. But it doesn’t. It’ll return user id with a bunch of useless information. If you want to export the tasks into a SharePoint list, you must turn the user id into email first, and only then create the item.
The basics of this solution were already described in other posts which I’ll reference.
Convert the user id into email address
As already mentioned, the first step is to turn the user id into email address. The approach is similar as when exporting users from Planner tasks to an Excel file. If you follow that post, you’ll get to the chapter “Fill the mapping table”. The original post is creating a mapping table with user names, but to update them in SharePoint item you’ll need user emails. To achieve that you want to store the Mail property, not the DisplayName in the variable.
addProperty(variables('var_mappingTable'),item(),outputs('Get_user_profile_(V2)_-_get_user_by_userId')?['body/Mail'])

The mapping table will then have a format as below.

Use the mapping table
The second difference will be when updating / creating the SharePoint item. The goal of the Excel article was to create a readable string with user names. But to create a SharePoint item you must follow the desired format.
[
{ "Claims": "user1@company.com" },
{ "Claims": "user2@company.com" }
]
Therefore, when you store the user information in a variable, don’t save just the expression (user email). Append the whole key-value pair, including the brackets.
{ "Claims": "variables('var_mappingTable')?[item()]" }

Then just switch to the ‘Input an array’ option and use the variable to store the assigned users to SharePoint.

And don’t forget to empty the variable after each created item.
Full flow diagram
Only the actions that are different from the export to Excel flow are expanded.

Summary
When you export Planner tasks with Power Automate, the assigned users can cause a headache, and not only if you store them in a SharePoint list. You must take the user id, convert it to more useful user information, and then use it to export the task. But the good news is that the processing is very similar, no matter where you export the task. It can be an Excel file, it can be a SharePoint list, or just a simple email with HTML table.
Hi,
Thanks so much for your extensive work to help others.
I’ve tried the above but I’m getting the following error message:
Flow save failed with code ‘InvalidTemplate’ and message ‘The template validation failed: ‘The action(s) ‘Get_user_profile_(V2)_-_get_user_by_userId’ referenced by ‘inputs’ in action ‘Compose_-_fill_mapping_table’ are not defined in the template.’.’
Can you give me a steer?
I’m very inexperienced so it’s probably something obvious no doubt.
Thanks,
Garry