Is it allowed to join a clan with an alt account when your main is in an another clan?

possible but frowned upon

And doing clan wars with that alt account is ok too than?

No, that's like farming.

i dont mean main clan vs alt clan. i mean just normal clan wars with the alt account because the main clan doesnt do wars.

Having an alt account in another clan is legal. However, it is frowned upon by most. You can also do wars on your alt like if it was another account. The only problem would most likely be if you faced yourself in a clan war.

Thank you for that rapid help