If you have an Android device start with Live Transcribe by Google. You’ll basically have the app open on your mobile device and near the audio source (Tip: for improved captioning, you can plug an audio cable directly into the phone from the PC – cuts down on any background noise).
Otter.ai would be the next recommendation and their Basic plan is free. It’s good for 600 minutes of transcribing per month.
Be aware that Zoom is one of the few platforms that does not provide auto-captioning, so options are limited. It is often up to the host of the event to hire a third-party captioning provider (i.e. AI-Media).
An upcoming device is SpeakSee, which is a device that features a set of microphones and an app that translates speech into text for the deaf/hard of hearing community. They have just announced today a new feature called AutoCaption: https://speak-see.com/pages/products-speakseeautocaption, which will allow for captioning on various platforms (i.e. Zoom, Google Meet, etc.).