I feel like this needs to be pushed back on a little bit. Don’t let perfect be the enemy of the good. Having a password manager that provides good passwords and TOTP as a second factor is way better than only using a password.
Sure, it would be nice if you had two devices. A phone password manager and a usb security key, but for many people it is inconvenient to carry a security key to plug when you need it. I’d rather that person keep a TOTP on their phone in that case rather than not use two factor due to inconvenience.
Your concern is mostly about “what if someone steals your phone or computer” then they have both factors. However, your average person isn’t getting hacked by someone they know, and random local thieves aren’t typically sophisticated enough to do more than re-sell stolen computer equipment. The average person is getting hacked by some dude in a foreign country who dumped a password database or phished a password. That person isn’t stealing your device so the fact that both factors are in the same place doesn’t really mean anything.
Also, most password managers are locked by biometrics these days. In that case, it isn’t really the app that is the second factor. It is your fingerprint or face. Someone may steal your device, but if they can’t get into the password manager that needs a password and biometrics then they don’t have anything.
Just wait until you learn that if you are going to use removed finger-tips then they don’t necessarily have to be your own…