I am trying to find that out as well. I don't have (no longer have) a Facebook account at all. I didn't trust anything that got posted there. I know of a lot of communications means that are a lot more secure than Facebook.. A few that come to mind is 'Private group on MeWe', our own server on Discord, and sms messaging via 'Signal'.. the last of which is encrypted end-to-end. An inquisitive investigator might be able to see that Person A sent a message to Person B.. but he won't be able to see what was in that message.
Hopefully others, more knowledgeable than I, will jump in here and give us some additional info.