You have to jump through some hoops (install Trezor Suite which allows bech32 addresses (bc1q.....) so Wasabi & Trezor can exchange info), but it all works. I set-up a dummy account, and it works.
Nice tool for backing up a Trezor if/when it comes to that. Recommended!
Noting is stored on any server. The keys are derived algorithmically (deterministically), even when the 13th (or 25th) passphrase is used. Everything happens locally, according to BIP39. The only "storage" is in your brain, or wherever you have decided to back it up (paper, etc.). So, there's nothing to worry about. The only thing you want to backup is the set of 12 (or 24) seed words, and the passphrase. Nothing else, and never online.
Nothing is stored inside anyone's server, Trezor's or otherwise. The only time the seed words/passphrase are exposed is when they are generated/chosen for the first time when you set up your Trezor. Your Trezor is directly equivalent to a paper wallet, and your wallet can be fully restored when you have the 12 (or 24) seed words, and the passphrase, even if Trezor's (or any other company's) servers completely disappear from the face of the Earth. The only other thing you need is the BIP39 specification, which is freely available and can never be lost.
It's a bit difficult to grasp at first, but once you understand it, it all becomes crystal-clear.