With classic I have used making a read only field required and programmatically filled it in as you have.
The Kinetic configurator still has a number of issues so don’t accept behavior that worked in classic but not in Kinetic. If something worked in Classic it should work in Kinetic.
I suggest opening a ticket.
Another approach I use instead of setting a control as required is to have a text box that I fill with messages and the like telling user what they need to correct. if they correct everything the text box will be empty. This way I can craft detailed explanations of what needs to be addressed. Such as “Control X must be greater than Control Y.” Or “An entry in Control X is required”
Then as part of the Page On Leave code I test to see if the textbox is empty. if Not i set args.Cancel = true preventing them from leaving until they resolve things.