At least right now, there is a literal add_watermark function, so probably easy enough to remove that surface level. Unless they added something cute to the training data to poison the well.
The readme on the linked github reads: “MyShell reserves the ability to detect whether an audio is generated by OpenVoice, no matter whether the watermark is added or not.”
Ah, thank you. Guess that's OK that the company/service do whatever they want, the paper/technique doesn't involve watermarks, so it'd be easy to remove/modify whatever they do in the library/service itself.