For staking wMEMO in the farm it’s a 2 steps process
To approve contract interaction
To deposit your wMEMO in the farm
Your first time staking in the farm contract you only need to approve once and after that it won’t ask you again, if you have already approved but the button doesn’t change to stake wMEMO, refresh the farm page, if it still doesn’t change clear cache, cookies and restart your browser then try again.
As for whitelist - it’s for upcoming redemption (Q3R) if you want to take part in redemption on 1st of October you will need to get your wallet with wMEMO whitelisted to redeem at liquid backing + basket of tokens.