privacyguides recommends Raivo OTP, see https://www.privacyguides.org/en/multi-factor-authentication/
Raivo OTP is a native, lightweight and secure time-based (TOTP) & counter-based (HOTP) password client for iOS. Raivo OTP offers optional iCloud backup & sync. Raivo OTP is also available for macOS in the form of a status bar application, however the Mac app does not work independently of the iOS app.
Its Github repo is at https://github.com/raivo-otp