I don't know if this can help everyone, but it worked for me.
Make an Instagram or Twitter account with your name and face, don't hide your identity, then start uploading walls of text expressing all the opinions and things that cross your mind no matter who is looking at you, I did this and it helped me deinhibit myself
At first I felt a certain embarrassment and nervousness at seeing people I didn't even know see my profound opinions, but over time I developed more tolerance for being exposed in public.
This is the key > develop tolerance to social pressure
Over time you will stop giving importance to what others may think of you.
Do this until you feel that it no longer makes sense to continue expressing yourself on social media.
This can be a great first step for very inhibited people.
Maybe it sounds like social suicide... but there is light at the end of the tunnel.