Calculate Formula for Rollupsum total likely amount of assigned user

In theory, we might have been in a position to set up a two steps calculation - a) to employ a custom calc field in Users module to rollupSum Likely amounts of Opps that are assigned to the User, and then b) to employ a custom calc field in Tasks to get that User's field value calculated via task assigned_to relation
But unfortunately, I was unable to find Opportunities in the list of modules available for the rollupSum in Users module to perform the first step.. maybe other clubmates will be luckier...

Nevertheless, my question would calculate the total of all Opps Likely on the Task record is created and/or/both edited may help to solve the business task?
If so, the logic hook configuring may help - let me know the name of the custom field in the Task module you'd like to put the value calculated

Thanks for the reply, the field in the tasks module is YTD

I see what you mean, Opportunities is not an option in the related field of the user module.

WOuld have been a good way to do it if it was.