This tool for retrieving data from public Facebook Groups via Facebook's API makes use of the fb_scrape_public library for Python 3.
Put fbg.py in a directory alongside a file named groups.csv. The groups.csv file should have two comma-separated columns representing group name and group ID. The first (header) line should read: group,id.
Open a Terminal prompt in the working directory and run the script with
$ python fbg.py
Data collection will start, and a separate csv file for each listed group will be saved in the directory. When all csvs have been saved, the script will also create xlsx versions of them, before shutting down.