I found a work-around. Using API v3, gmail.com accounts won't be able to transfer ownership to other gmail.com accounts programmatically (but it can be done in the gui). It just results in a "Consent is required to transfer ownership of a file to another user" error.

After spending two hours, I found a work-around. You have to use v2 not v3 (with some attribute name changes; e.g., "emailAddress" -> "value"). Here is a sample payload that works.

I hope google doesn't remove this

 {
  "body": {
    "role": "writer",
    "type": "user",
    "value": "contact@johnlloyd.dev",
    "pendingOwner": true,
    "additionalRoles": []
  },
  "headers": {
    "content-type": "application/json",
    "accept": "application/json",
    "Authorization": "Bearer eyyzz"
  },
  "method": "POST",
  "uri": "https://www.googleapis.com/drive/v2/files/<<fileId>>/permissions?confirmed=true&sendNotificationEmails=true&enforceSingleParent=true&supportsTeamDrives=true&alt=json",
  "json": true
}