Thanks for the hints - but I have not found the solution yet.
Both of the apache versions have the same .htaccess file. It is a single line -- "AddCharset UTF-8 .txt"
The php on the Pi2b+ is
PHP 5.6.40-0+deb8u12 (cli) (built: Jun 28 2020 18:04:15)
The php on the Pi3b+ is :
PHP 7.3.19-1~deb10u1 (cli) (built: Jul 5 2020 06:46:45) ( NTS )
Both servers have 2 versions of php.ini - 1 in the /etc/php/cli directory and 1 in the /etc/php/apache2/
My explanation of the problem did not fully state what I am doing. The function of the Pi2B+ is a WU weather camera feed. I made no attempt to move any web application from the old server to the new, so I did not attempt to transfer any configuration files. The Pi3 is also my backup for Weatherlink6.0. It uses weewx utilities / mariaDB to put the wlk files into a sql database.
The Pi2 gets a image from a web camera with a wget, gets the weather data from a Meteobridge, uses 'imagemagick' to combine the two and then it ftps the result to WU. The txt file is the results of that process so that I can see how oftern WU refuses the file. The other task on the Pi2 is receiving pictures from a camera monitoring a driveway and several wildlife cameras. A cron job runs multiple times per day to build a photo album - images separated by date and with thumbnails ('album' is the program). I have upgraded the weather camera and I am in the process to set it up on the Pi3 and then turn off the Pi2 process when I am happy with the new. It is a pain to look at txt files on a tablet or phone by downloading to the device and then opening.