It may or may not be blank.
Fediverse servers work like this: servers only notice accounts from other servers if someone follows or interacts with them. If no one on your server has ever followed an account on another server, the account may appear blank to you.
The reason servers work like this because of resources. If servers had to keep a copy of every post from every user on all the thousands of Fediverse servers in the world, their running costs would become prohibitively expensive (and most of those posts would probably never be read anyway). This means people on very new or very small servers may sometimes see blank profiles even for popular accounts that have been around a while.
Viewing the latest and most complete version of an account
To check what the profile really looks like, log in to your account through the website, go to the profile, click on ︙ and then “Open original page”. This should open the profile in a new tab on its home server, which will show all the public posts the account has ever made.
Unfortunately, original pages on other servers are more difficult to interact with. By default your have to enter your username and password each time, though there are ways to make it much easier.
Backfilling to the rescue?
Fortunately there may be a possible solution on the way called “backfilling”. This would mean as soon as you follow someone your server would automatically check the account for past posts and display some or all of them on your server. With backfilling there would never be blank profiles, and there would be much less need to fiddle around with original pages. At time of writing backfilling is the most popular suggestion on the Mastodon github site, and if you’re comfortable using github you can go and give it a thumbs up ⧉.
How to prevent your profile from ever looking blank
If you pin some of your posts to your profile, these will automatically be backfilled, and your profile will never appear blank to anyone. You can pin up to five posts on a profile, and these can include attached photos, video and audio, so they’re a great way of introducing your account to potential followers. Click here to find out how to pin posts.
Accounts with restricted post visibility
An alternative reason why a profile might be blank is this: if the account has follower requests on (indicated by a padlock 🔒 next to their name), and all its posts are followers-only, then you will not see any posts on their profile until you follow them and your follow request is accepted.