Yes you must have to connect your Trezor safe 5 to the computer to create seed.
Just comment your Trezor safe 5 wallet to the USB and open Trezor Suite and Install firmware and then simply create a wallet.
But always remember this, not your key not your crypto so always keep safe your seed phrase on secret zone and do not share it to anyone. if someone get your seed then he can directly access your wallet and move your fund without any authorizations.
Honestly, it kind of makes me want to look elsewhere for another device. Why would you feel comfortable with your device connected during the most important part of setup(releasing seed phrase)?
Well personally, I would rather just generate the seed myself and then import that into the hardware wallet device directly through its own user interface.
I wouldn't trust hardware wallets to generate my seed phrase due to the risk of tampered firmware.