All communication platform provides you with a feature where you can block someone when you want. But, what if someone blocks you on Facebook? There are many ways by which you can see who blocked you on the Facebook app:
1. If someone blocks you, you can’t search for that person on Facebook search.
2. You can not send messages to the person if you have been blocked by them.
3. Moreover, you will not be able to tag a person anywhere if you have been blocked by them.
4. The person will not see in your friend list and you can not see their profiles.
Source:
https://getassist.net/who-blocked-you-on-facebook/