There are no multi-image post modules for the LinkedIn app.
According to the LinkedIn documentation, you’ll need to individually upload each image asset first using
POST https://api.linkedin.com/v2/assets?action=registerUpload
Then attach the items to the share
POST https://api.linkedin.com/v2/ugcPosts
You should be able to integrate the two endpoints in Make using the generic LinkedIn “Make an API Call” module.
You can also suggest for it to be made in the Idea exchange. Don’t forget to search for it first, in case someone already suggested it!