Cloud recordings

Pinning is a local function only - spotlighting will do what you're looking for when recording to the cloud or attempting to force prominence to all participants.

From Zoom KB:

Pinning a screen allows you to disable active speaker view and watch a specific speaker. Pinning another user's video will only affect your local view, not the view of other participants, and it will not affect cloud recordings.

Spotlighting a video puts a user as the primary active speaker for all participants in the meeting and cloud recordings.

Moving forward, you should be able to get what you need on your cloud recordings by spotlighting, rather than pinning.

For your existing recording, your options are limited. You may be able to crop a lower-resolution slice of your gallery view (using a 3rd party NLE like Adobe Premiere, Avid MC, FCP, etc) to manually 'grab' the participant's video that you need and then impose it into the active speaker recording. This isn't a great solution and relies on you having a copy of the gallery view, some type of NLE, and the required time/expertise.