Could you describe your problem in more detail?
Microblogs are always associated to your profile. If you want to post something which is not meant for a specific magazine, the random magazine is what you need to use. It is a pseudo-magazine (and so not federated as a community) which aggregates all microblog posts which are not attached to a real magazine.
What exactly do you mean “to a profile”? Can you give an example of the difference (I never used Mastodon)?