To add summerize field in related list, please follow the below steps:
From the PWR related list configuration, click on the '+' button below the "Summarize Fields"
Provide a name and select the aggregate operator from the list
Select the field on which you want to perform the aggregate operation
In filters, select the appropriate filter as per your requirement
All records - It will calculate for all records
Custom Filter - It will calculate only for records that satisfy the custom criteria
Dynamic filter - The dynamic filter works for both static and additional filters.
Page Records - It filters the records connected to the selected object.
Click on the Save button
Now you will be able to see the added summarized field in the preview section
