Interviews are a poor measurement instrument, and both sides know it. That is an advantage if you prepare for the interview that actually happens rather than the one you imagine.
Most of it comes down to five things, none of which require you to be a naturally good talker.
What to prepare
Have three stories ready that you can tell in two minutes each. Know the first question you would ask about the role if you already had it. Be able to say why this job and not a similar one elsewhere. Prepare one thing you got wrong and what you changed afterwards. And read the job advert again on the morning of the interview, because half of what they will ask is already in it.
“The best answer I heard all year was someone explaining a project that failed. She had clearly thought about it for a long time.”
Wren Castellanos
Rehearse out loud at least once. Everything sounds fluent in your head and noticeably less so the first time you actually say it.