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)?
I understand you very well and I will feel the same way too because I don't want to have anything to do with me connecting my hardware wallet to my pc for anything, this is why I choose Keystone wallet.
It's air gapped, you don't need the Internet connection to make transactions and when it comes to updating the firmware you are given the open to keep your device as an air gapped and instead download the firmware on a memory card and insert the memory card into the hardware device and update.
No Internet connection is needed to complete the update which makes it way more safer than few hardware wallets out there. If you don't like the idea, then look for devices that are made like smartphone, with full phone like operational screen. E.g
Their updates are mostly offline, or straight in the hardware itself, no need to connect to PC.