Not sure how the sizes compare to the Kappa shirts of 2019/20, so don’t know how helpful this is to you, but I have the green and black third shirt from that year, it’s a medium and regular fit but I would say it’s definitely more ‘slim’ than regular. I’m erring on the slim side at 5ft 11 and 11st 4, and it fits me nicely but I suspect a slim fit Kappa might look spray-on on most people.
Seems that Kappa stuff in general is on the small / slim fit size so I’d be nervous about ordering a slim fit.