If you tried to cash out and you are being told that you are short of BNB to cover the gas fee, you can try to swap the coin to BNB see if it's enough for swapping to BNB native coin, then you can just cash out the BNB and the fee will be deducted still in BNB. If that process does not still work, then you have to deposit more BNB to your MetaMask wallet just like you have been instructed by MUGNIA.
I think in this case there is no other choice but to deposit extra BNB to carry out transactions because not all wallets have the same function as that. I think OP has been successful with his transaction because I see there is no response from OP anymore.
It's almost a year ago when OP made this post. Whether he was successful or not, there's no clear explanation.
However, the best thing is that many people can learn from this case, that when you want to carry out transactions on personal wallets, especially when making purchases, swaps or transfers on personal wallets / DEX / others, a fee is required. Because this is BSC, the fee used is BNB and it is relatively small.
Actually, one way is to send BNB from another wallet or buy it on an exchange. For now it seems that sending BNB as fees in small amounts from exchanges is no longer difficult. In fact, many exchanges do provide a minimum sending limit that is quite small so this is quite helpful for those of us who want to send a fee.
However, the problem is that if the token is an ERC20 or Ethereum token, which is known to require a larger fee. But if it's BSC, then you just have to send BNB from the exchange. Or sometimes, there are parties who sell retail BNB / retail ETH and others for small amounts and reasonable prices.