Priority Formulas Receiving Mirror Columns Error

Hi! I recently set up a subitem formula where the priority will change based on how far away the due date is.

I am now looking to set up an item formula that shows the most “serious” subitem priority on the main item.

For example, if one of my subitems is “Critical” in priority I would like the main item priority to be set to “Critical”. If there are no “Critical” subitems but there are “High” priority subitems I want the item to be set to “High” and so on for “Medium” and “Low” priority subitems.

When I create this formula on the item level I receive a message saying that mirror columns are currently not supported in formulas. I saw someone that did this this other way around by using the AutoBoost app, but I can’t figure out if any of their automation templates would help.

Thank you so much in advance!