I believe you need to convert the cookies to the format that BAS understands, and then import them into BAS using a standard method.
Take a look:
https://chromedevtools.github.io/devtools-protocol/tot/Network/#type-Cookie
I am running the steam registration page with the load action but HCaptcha is not showing up so I guess it is related to the browser embedded in the bass because with a normal browser the registration page works successfully.
Am I missing something or is the BAS broken?
Unable to reproduce the problem. Please describe in more detail how this can be reproduced intentionally.
Please attach a test project that reproduces the issue.

@docker0004 disable recaptcha module if its active
@docker0004 If you try to register an account as is, will there be an error? I mean, maybe you shouldn't have a captcha?
Please attach a test project that reproduces the problem.