Blockstream Green Wallet Security
Part of the design is that compromise of their service is a little bit pointless. They can not sign transactions spending your money to begin with, as the transactions also need a signature from your wallet too.
There’s no scenario in which the service can spend your money without your participation to some degree. In unlikely scenario the service attempts to force you to sign a transaction, you wait for the timeout and spend your money using the backup tool you linked to.
As with any wallet, if you lose both the seed phrase and the wallet on your phone your money is lost, those are the things which identify your money. To avoid this as a problem, don’t allow that to happen.