I clicked on Facebook/Twitter/LinkedIn/Instagram post in Publish editor, but it won't allow me to edit my post
Please open your browser as a Private window mode and try again. It sounds like you're experiencing a plugin/extension conflict.
Click on the text of your message in the Facebook/Twitter/LinkedIn/Instagram preview and it should convert to an editable field.
Another solution is to use a different browser versus a private window or you can start disabling each of your browser extensions until you find out which is conflicting, then see if that has an update available.