I wrote a TOTP library and a client program that uses this library (in C - as an attempt of learning C) to make the desktop tool compatible with andOTP encrypted files. Things went well. I was able to get OTPs from andOTP encrypted JSON files. But I am unable to get time to work on it further. The code is open-source. It was fun :)

https://gitlab.com/grijul/libzotp

https://gitlab.com/grijul/zotp