

Salesforce users cannot create Kanban salesforce views on formula fields.
A workaround is to create a picklist field that imitates the formula field.
Add the new picklist field on your Account page layout before selecting the field as a “Group By” option under Kanban Settings.
Considerations for Using Kanban In Salesforce
Create a Picklist field that holds all formula field values.
When a Kanban view has to be created based on a formula field, Create a picklist with all possible values of the formula field and hide it from all users using the “Set Field-Level Security”. Make sure the picklist field is placed in the page layout.
Now, create a time-based workflow that automatically updates the picklist value depending on the formula field.

You can now create a Kanban view based on this picklist field
Easy to implement, easy to migrate, Kanban view is indirectly based on formula field.
the Kanban system as a way to manage work, including Flexibility. Focus on continuous delivery. Reduction of wasted work / wasted time. Increased productivity.
Every formula field which should have a Kanban view associated with it must have a picklist field.
Using this workaround, Kanban can be set up for formula fields.