A collab post on Instagram is a shared post created in partnership between two or more accounts. When one account creates a post and tags another account as a collaborator, both accounts appear on the post, and it shows up in both feeds.
Here's how to create a "Collab Post"
Go to create a post on Instagram as you would any regular template or photo
Tap the "+" icon at the bottom of the screen to create a new post.
Choose a photo or video from your gallery
Click "Next"
Edit Your Post:
Make any edits you want + write a caption.
Tag Collaborator:
On the screen where you add captions, tap "Tag People."
Select "Invite Collaborator" and search for the account you want to collaborate with.
Once you find the account, tap on it to tag them
Share the Post:
Tap "Share" to publish your collab post.
The collaborator will need to accept the invitation for the post to appear on their profile.