Make sure you throw that mit away!
You shouldn't use a clay mit to wash the car, but only use it to remove bonded contaminants after you've got the car has been thoroughly cleaned.
Clay/mits nearly always leave some degree of marring and ideally the car should be polished afterwards. Any marring will obv. be more evident on darker paint that on light colours or silver.
I collected my car from BMW last week (after it's first MOT) and it was all clean and shiny again. Unfortunately I parked it under one of the lime trees on the street where I park and several days later it was completely and utterly caked in tree sap. Put it this way, the electric tailgate refused to open!
As I park on the street, I can only use a bucket to clean the car (and I'm fresh out of butt water atm) so (after work) I mixed up a strong-ish solution of Carpro Reset shampoo (which is really excellent), sprayed the car with a bottle of bug and tree sap remover that I had kicking about and I got 99% of it off using a noodle mit without too much trouble.
The following day I gave it a second wash and then a wipe down with Bilt-hammer Cleanser-Fluid and that got it proper clean ready to apply then graphene sealant. There were a few bonded bits so ideally it could have done with a clay as well but I didn't have time to polish the whole car afterwards so that can wait until later in the year.