Its a personal space of a person and its not mandatory for a Assistant Professor to be active on social media platforms. So if you don't like you can obviously ignore it. Now, there can be some awareness programs or outreach programs in which the college may ask you to give a talk on the social media platforms regarding some topics, for that case you may need to know a bit about the system or you can learn it anyway. So its not mandatory for an Assistant Professor to be active in social media platforms like Twitter, FB, Instagram. Now regarding LinkedIN, if you are interested in getting somewhere else a new job then it can be really helpful as there are many professionals who use to recruit there. SO if you do LinkedIN it can be helpful for you to update your career but also its not mandatory.

I hope this answer helps. All the very best for your future endeavors!