That depends on the settings you make and the data you publish.
For example search engines can access your profile, but by default only to the most important data. You can change the settings so that visitors (including search engines) can see more data about you. Or do you limit your profile so much that search engines can access only very little data about you (this is the default for children under 15 years).
However, if you e.g. publish a post in a group, which is accessible for guests, then also search engines can access this post.