The extention will only show the L2 gasfee on signature UI while there is a 2nd L1 fee involved. This makes TXs look amultitude of times cheaper then they are in reality. The only way to notice this by missing eth or visiting the explorers.
Hey @F.icey, thank you for the feature request! In the meantime, if you are looking for the total fee involved in a bridge transaction, often times the bridge dapp page indicates the total amount required. You can also get an estimate of the fee on L1 through a gas tracker like 36 Gwei | Ethereum Gas Tracker | Etherscan.
To clarify, a 2nd L1 fee is only involved for bridge transactions, because you also need to pay gas fees to withdraw the funds on L1. Other transactions on L2 would not require these 2nd L1 fees and the amount shown on MetaMask would be the only gas fee required.