they still have not fixed this

Me too. I even tried the "special" cosmetics, not the regular full art ones and had 4 different cards out at the same time. But nothing.

Same here. Like koieokei#37186, I made a deck with only cosmetics and it did not help.

Not working for me as well. Tried various different decks and even constructed a deck with just cosmetics.

Just weighing in to voice that I also am still having this problem.

Same problem here. Several games with ONLY cosmetics equipped even. Vs players and bot both... Winning/losing/etc. Making sure I PLAY 4 different ones even. This achievement will not trigger for me.

Same problem here - I've played several games with more than 4 cosmetics in use (sleeve, avatar, title, companion, stickers and phrases, plus card cosmetics (which may or may not count)) and have not received the achievement.