Thank you! I have been having this exact same issue and could not find any solution. Garr's 'thank you' comment is what I needed as well as there was no easy way for me to figure out how to add httpd to the list of applications. The missing link was using finder to drag httpd to the Full Disk Access window in the System preferences section.

Note you must dismiss the finder window which opens when you first click the + on the Full Disk Access to add a new application. Then you can proceed to drag httpd from your finder window to this FDA section.

Thank you both for providing this information. Much appreciated!