I deleted my Facebook account back in 2017. If you still have an Facebook account, maybe think again if you really need it. There's this site and Kev Quirk also wrote a list of reasons why using Facebook might be a bad idea.
Although I have no Facebook account anymore, I still use WhatsApp and Instagram. WhatsApp is really popular in Germany (despite being owned by Facebook) and without WhatsApp you would socially exclude yourself from too many things. All university groups are coordinated via WhatsApp - although I study computer science and people there have technical knowledge, it's sad… I only use it for group chats though, because almost all my contacts use Telegram.
In the past I used Instagram to share moments from my life, stay in touch with some people and get to know new people, but since I've been in a happy relationship, my Instagram usage decreased to almost zero. I will probably export everything and post pictures on PixelFed or maybe a section on my website or blog instead.