For this point release, we fixed an issue that was published with Jetpack 6.4, which affected visitors attempting to comment by authenticating with Social Login buttons on the Jetpack Comments form.
The full changelog has more details on this update, and we’re able to answer questions via our support channels.
Thanks for your support!
Jetpack 
There should be an option for commenting on the website if I have logged in in wordpress.com account. There is no option to comment with social credential if I have logged in in wordpress.com.
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Thanks for reaching out to us about this! To use this feature, Jetpack’s Comments form needs to be activated, and you must also allow visitors to sign in using social networks. We detail this here:
https://jetpack.com/support/comments/
If you run into any issues, we’d be happy to take a closer look – just give us a shout here:
https://jetpack.com/contact-support/?rel=support
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