Aegis on Android via F-Droid - https://f-droid.org/en/packages/com.beemdevelopment.aegis/
Raivo OTP on iOS - https://apps.apple.com/app/raivo-otp/id1459042137 It has a Mac App too which just reflects the OTP and not doesn't store data on it.
Both are FOSS. Both allow to copy seed. What else one needs?
Here's a good video about TOTP by Techlore which explains why going with Authy is a bad idea - https://www.youtube.com/watch?v=iXSyxm9jmmo