Hello @fleur2
You might need to use this reference table to convert priority values.

Full documentation here: https://learn.microsoft.com/en-us/graph/api/resources/plannertask?view=graph-rest-1.0
Priority returned by Planner is usually in integer format. You just have to convert it manually. For example, you can a Label control and its Text value, you can add the following code:
Switch(
ThisItem.Priority,
0, "Urgent",
1, "Urgent",
2, "Important",
3, "Important",
4, "Important",
5, "Medium",
6, "Medium",
7, "Medium",
8, "Low",
9, "Low",
10, "Low",
"Unknown"
)