I have 0 Eth on my Eth Mainnet. I have ~6 BNB that I sent over BEP20 (Binance Smart Chain). It shows up properly on my Binance Smart Chain Mainnet.
If I switch to my Ethereum Mainnet it shows I have ~6 ETH (same amount as my BNB) there where I have 0 and even calculates the ~ $ value of ~6 ETH. I have checked on Ethscan. The actual wallet address has 0 Eth on the ETH20 mainnet.
I have transacted without issues (checked on bscscan) on the binance smart chain mainnet.
I am running MetaMask 9.4.0 on the Brave browser (Win10).