You can allow anonymous access in your instance, but in this case, if your instance is open in the internet and not restricted to your network, anyone will be able to view the data.
If you want to have restrict access, with username and password, then you will need a license of each user, even if they do not add new data to the instance.
In the permission scheme, use the group "anyone" in the "browse" permission - people will then not be required to log in to see the issues in the project, and that sort of access requires no licence. The users are anonymous.
Two recommendations though
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