Version of Apache installed on a Debian machine

Try apachectl -V:

$ apachectl -V
Server version: Apache/2.2.9 (Unix)
Server built:   Sep 18 2008 21:54:05
Server's Module Magic Number: 20051115:15
Server loaded:  APR 1.2.7, APR-Util 1.2.7
Compiled using: APR 1.2.7, APR-Util 1.2.7
... etc ...

If it does not work for you, run the command with sudo.

For me apachectl -V did not work, but apachectl fullstatus gave me my version.

Or, less directly:

nmap -A localhost -p 80

works in debian 11 bullseye

/usr/sbin/apache2 -v