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For the seed, this is not a problem because many useless words are entered and the right words in your seed are entered in a random order. The chances that someone watching your PC will find the right seed are extraordinarily low.
Buy the model T if you don’t want to write your seed on a PC.
For the passphrase, by itself it is useless. It must be used with your seed, which is on your Trezor to generate your hidden wallet. The same passphrase with 2 different seeds will generate 2 completely different wallet.