I do not know if I'm in the right place to talk about Wallet's but I have a burning question to ask. How Trustworthy is Trust Wallet ?
Trust wallet is owned by Binance, and I think it's one of the best non-custodial wallets on mobile devices, trust wallet security on the part of trust wallet itself is good enough, atleast, I've used trust wallet since its inception and never had issues.
But it must be told to you that the security of your non-custodial wallet, be it trust wallet or any other wallet is largely in your hands, it is your responsibility to make sure your private keys or seed phrases are written down properly and kept in a very secure place where no one can access it except you.
Also, how can I back Trust Wallet Address? Just if Someone misplaced his/her mobile.
By "back", I am guessing you mean, backing up your seed phrase or private keys issued to you by trust wallet, if this be the case, then I think the best way to back up your seed phrase is to write it down and keep it somewhere very secure, this is what I already said above, there is no other way I can think of right now that is safer than writing down your seed phrase or private key, (you have to be very careful when writing it down in order not to make any mistake) and keeping it somewhere that is very secure and away from preying eyes.
What advice would you give any ( usage of wallet ).
Hardware wallets, otherwise known as Offline wallets I think are the best in terms of security, since like it's called "offline wallet" means it's offline when not in use and can not be hacked by scammers and you don't have to worry about how to keep your private keys or seed phrases safe.
And to add, aside trust wallet, if you own your own desktop computer, you can try out Wasabi wallet, it's also one of the coolest Bitcoin wallet in the space.