Do i need a subscription to game pass to crossplay grounded if i purchased it from the...

If you're playing on PC, Game Pass is not required to play online.

You need the PC Game Pass or Ultimate Game Pass subscription to use this game.

This game is part of the Game Pass catalog, it is not a game that was offered with 'Games With Gold' and you also do not need a Live Gold subscription to play online on PC.

To summarize you can either subscribe to Game Pass for PC or Game Pass Ultimate to use the Game Pass catalog or just buy the game from the Microsoft Store app on your Windows. If you purchase the game, no active subscription is required.

If you do not have the game, you will need to purchase it or renew your Game Pass subscription

Anything you download from Game Pass, you can play while it's on Game Pass and while you have a subscription. Once it's removed from Game Pass or your subscription expires, you cannot play the game unless you purchase them game. If you purchase a game
while it's on Game Pass, you do get a discount on the game and you can continue playing it after your subscription ends or it leaves Game Pass.

If you have been playing DayZ on Game Pass Ultimate, then when you downgrade to Core, the game is not included. You will either have to purchase the game, and then you will be able to play online with Game Pass Core, or purchase Xbox Game Pass or Game Pass Ultimate to continue playing the game from there.

On another note, you do not need a subscription to play online multiplayer on the PC.