@Jon Tan (Airbyte) is there an update to this answer?

Yes there is, if you use the https://reference.airbyte.com/reference/workspaceoauthcredentials endpoint to set your source OAuth credentials for a workspace, you can bring your own creds and create your source using tokens that you generated. See https://reference.airbyte.com/docs/creating-oauth-sources for more info (Approach 2). We are currently working on allowing approach 2 in the linked doc to work through browser authentication as well.

Is the guide here still up-to-date: https://reference.airbyte.com/docs/creating-oauth-sources?

Yes it is current although I hope to invalidate it soon by allowing workspaces to create oauth sources using either approach