Hi,
Following your message, I look into the developer documentation of hCaptcha and I actually found that they use the same API as ReCaptcha. They actually even have a documentation page to modify the code made for ReCaptcha to work for hCaptcha:
docs.hcaptcha.com/switch
So I took the time to make a copy of the Recaptcha plugin, rename everything from ReCaptcha to hCatpcha and test it.
Here is a first version I could successfully test on the registration form of the HikaShop checkout:
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So install it and configure it via the Joomla plugins manager and it should work.
Let us know how it goes so that we can add it officially on our end.