A Password Manager is a must in today's world, but if you can protect yourself further with more than just a password, like two-factor (step) authentication (2FA), then do so. That said, do not use SMS based 2FAs, if you can avoid them.
Here are some good options:
Aegis Authenticator is a free, secure and open-source app for Android to manage your two-factor verification tokens for your online services.
Time-based, one-time Passwords (TOTP) from QR codes for two-factor authentication
An easy-to-use, open-source two-factor authentication app designed specifically for iOS
Bitwarden is not just a password manager, but can also handle your 2FA
iOSDesktopCli
Strongbox is not just a password manager, but can also handle your 2FA
Open-SourcemacOS
A native, lightweight and secure time-based (TOTP) & counter-based (HOTP) password client built for iOS
KeePassXC is not just a password manager, but has 2FA built-in.
KeepassDX is a password manager for Android, but has your 2FA built-in
Simple application for generating Two-Factor Authentication Codes.
Linux
Even better than using an app would be using Hardware Security Keys. The two best options are.
All-in-one configurable security key
With a simple touch, the multi-protocol YubiKey protects access to computers, networks, and online services.
Some YubiKey models have a wide range of features such as: Universal 2nd Factor (U2F), FIDO2 and WebAuthn, Yubico OTP, Personal Identity Verification (PIV), OpenPGP, TOTP and HOTP authentication.
Login to websites (e.g. Google, Facebook) using secure One Time Passwords (OTP), U2F or ordinary static passwords. Login to computers and network services (e.g. SSH) using certificates.
Email Encryption
Encrypt your emails with GnuPG, OpenPGP, S/MIME or your favourite email client. Keep your secret keys secure on your Nitrokey.
Encrypted Mobile Storage
Carry important data with you, hardware-encrypted on your Nitrokey Storage device (16-64 GB). Compatible with Windows, Linux and Mac OS.
Hard Disk & File Encryption
Encrypt your hard disks and files using TrueCrypt/VeraCrypt, GnuPG Tools and more. Keep your secret keys secure on your Nitrokey.
Key and Certificate Management
Protect your server certificates by using up to 300 cryptographic keys with the Nitrokey HSM. Ideal for security servers, Public Key Infrastructures (PKI) and Certificate Authorities (CA).
Server Administration with SSH
Manage your servers, critical infrastructure, and Internet of Things (IoT) not just securely but also more easily. Administrators no longer require to synchronize key files between their desktops or remember complex passwords. Nitrokey acts as a mobile latch key to your servers by using Secure Shell (SSH), providing 2FA always at hand.