One of the following apply to you:
Problem scenario #1
You sent ARB to an Ethereum address of you wallet. You cannot find it on the wallet. What should you do?
Problem scenario #2 (a more generic problem)
If you sent coins to an ethereum-based address of a Trezor wallet, but you are not using Metamask for those coins, can you create a new MetaMask wallet or do you need to import an existing wallet to get those coins?
Problem scenario #3
You want to know if you sent coins to a Trezor wallet that are not natively supported, are the coins lost? The wallet supported the blockchain type (e.g., ethereum).
Solution
You may need to import your wallet into MetaMask or a third party wallet (e.g., with the recovery seed). For ethereum-based cryptocurrencies, Trezor can give you an [ethereum] address. To view your balance of Arbitrum, you would need to import your wallet into MetaMask or a third party wallet. It is not the end of the world if you already sent ARB to an ethereum-based address without registering it with an ARB balance, but you would have to input your recovery key into a software wallet. After that you need to send a new amount of Arbitrum (regardless of how much as long as it is more than zero coins) to the wallet to trigger the original transaction's balance to appear. The first balance may be invisible until the second transaction happens after you use a wallet that supports ARB. Your total balance should be viewable after you do this. Recovery word seeds can be reset if you can put all your cold storage coins onto hot exchanges, then do a factory reset of the physical device.