I have been using Authy on desktop to generate TOTP for 2FA. Recently got a message that they are shutting down the desktop client. I tried looking for a stand-alone and simple (as simple as Google Authenticator) app for Windows but did not find any, so I built one myself. It can generate Time-based OTP and can also import the QR code exported from Google Authenticator.
Currently it supports only TOTP because that's what most services seem to use.
The app utilises -
OTP.Net for TOTP generation https://github.com/kspearrin/Otp.NET
ZXing.Net for reading QR codes https://github.com/micjahn/ZXing.Net
QRCoder for creating QR codes https://github.com/codebude/QRCoder
Google protobuf for reading Google QR code protobuf message https://github.com/protocolbuffers/protobuf
Utilising .proto file from https://github.com/scito/extract_otp_secrets