I had sort of the same problem.
My Z is a 2019 model that I bought new here in the Philippines. I only had about 5000 kilometers (3100 miles) on the bike when it began slipping badly. There were two reasons why I never tried to get it fixed under warranty. First is that I would have had to take the bike back to the island where I bought it by ferry then returned home and when ever I got it fixed I would have had to make the trip again to go get it. There are very very few motorcycle shops in the Philippines that sell anything bigger than 125 cc bikes, and 90 percent of them are scooters.
I ordered the thinner bearing, new pull rod, heavy duty springs, and competition fiber clutch plates. I do not remember who the actual manufacturer was but I ordered those from 2 different suppliers, one of them was in Italy. During installing those new parts every thing went smoothly until I tried to replace the outer clutch cover. It seemed that no matter how I tried I could not keep the internal clutch arm engaged properly while replacing the cover. I finally had to even order some gasket material in order to make a new gasket because I had it off and on so many times.
As everything takes so long to get shipped here I got a whole roll of the stuff so that I will be able to make any other gaskets I might need in the future. Sorry that I can't help you out with a how to as, at least for me, it was just a try and try again situation with some choice words and hair pulling to finally get it done.