We have a lot of projects configured in Jira Work Management.
We would like to adjust the policy so, every user in a project has access only in the issues where this user is Assignee, Reporter, Assignor or Mentioned.
Any assistance in this is kindly appreciated.
You won't be able to modify the permissions if you are on a Free plan.
Otherwise you can modify the Permission Scheme for the project. You might want to copy the existing scheme and then make the changes if you want to share the scheme across multiple projects.
You will need to play with the permission scheme of the project. Look at the browse project permission first but keep in mind that you can't assign permission to people mentionned in an issue unless you're using plugin like mention & watcher.