There are a few reasons why you might not have access to a subreddit. You may have been banned from the subreddit by a moderator. You may also not have access to the subreddit if it is private or restricted.
If you are banned from a subreddit, you will not be able to access the subreddit at all. You will not be able to view any of the posts or comments in the subreddit, and you will not be able to post or comment in the subreddit.
If a subreddit is private, you will only be able to access the subreddit if you are invited by a moderator. Private subreddits are typically used by groups of people who want to share content that is not appropriate for public consumption.
If a subreddit is restricted, you will only be able to access the subreddit if you meet certain criteria. For example, a subreddit may be restricted to users who are over a certain age or who live in a certain region.
If you are trying to access a subreddit that you do not have access to, you can try contacting the moderators of the subreddit. They may be able to grant you access to the subreddit if you meet their requirements.