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The seed phrase is the same for any set of addresses contained in that wallet. In other words, when you add an Ethereum address (or ten) or add a Litecoin address (or ten), or a Cardano address chain… these are all tied to the one seed phrase.
You can create new and unique wallets if you’d like to, and manage them with the same Trezor. However, this isn’t strictly needed. You may choose to do this for any number of reasons, such as creating a hidden, password protected wallet with your most valuable HODL assets and another wallet with play assets that you day trade. Again, not required, but could be useful to separate the assets into different wallets either for your psychological benefit or to obfuscate certain assets.