In a perfect world your 2FA secrets would be on a device that is separate from what you’re logging into, and not just accessible from any of your devices.
In reality… if you use the Standard Notes TOTP feature for your 2FA that is probably fine, because Standard Notes has end-to-end encryption, so you don’t have to worry about them accessing your codes. It is just a bit riskier when your codes are accessible from all your devices, you can decide whether that is worth it or not to you.