Social networks, as a whole, aren't prohibited in Ukraine. Only a couple russian internet services are blocked as part of sanctions against Russia. Because of the... you know... war.
Ukrainian here. Where did you hear that? Don't read news there anymore, they manipulate you. Ukraine introduced sanctions against russian businesses on its territory. As part of those sanctions, websites of three major russian IT companies have been blocked. That included Yandex (which is very similar to google, also has a lot of web services), and a couple of russian social networks.