Currently there is Guest role in gitlab which have many permissions like download projects,leave comments…
is that possible add a new feature like read only option which the user have only option to read the contents from the projects not to download or perform other actions.
the feature Auditor user is available in the Premium tier. You can see that with the marker on the right hand side which features belong to Core (CE) or Enterprise tiers. An overview of features can be found on the product website.