Instagram does not allow you to create a Collab post from Instagram.com or from Meta Business Suite on a computer.
Here is how to create a Collab post from a computer (desktop, laptop, web browser, PC, etc.):
Using OneUp (the social media scheduling tool) you can create a Collaborator (Collab) post on Instagram from a computer.
OneUp allows you to add up to 3 collaborators at a time on your Collab post.
OneUp is one of the only social media scheduling tools that supports Collab posts on Instagram. It also has a ton of other features. Check it out here: www.oneupapp.io