Just tap on a recording and select share.
Facebook app might not be able to accept ACR recording if you have upgraded to Android 8.
This is not limitation of ACR.
ACR has been updated to work with Android 8 where sharing file:// method is no longer possible.
Other apps such as Facebook would need to implement it.
You can test sharing any ACR recording to other apps that supports it and see that issue is not with ACR