Ente Auth is a free open source program for storing 2FA-OTP-tokens E2EE in a cloud and synchronizing them between various devices to generate codes there. Windows, MacOS, Linux, Android and iOS are supported. [1]
There is a ZIP version that requires no installation, but unfortunately it stores its data in the users home directory instead of the program directory, so it is not really portable. [2]
[1] https://github.com/ente-io/ente
[2] https://github.com/ente-io/ente/discussions/1957