Why should I hide my server software version?
Servers often announce themselves in the response headers: "Apache/2.4.41 (Ubuntu)" or "X-Powered-By: PHP/7.4.3". To an attacker that is a shopping list. Every version has a published set of known weaknesses, and automated scanners look for exactly these strings. Hiding the version does not fix a weakness, but it stops you being singled out by the cheapest kind of attack.
Why it matters
Most attacks on small business sites are not aimed at you. They are scripts scanning millions of sites for a particular vulnerable version, then attacking whatever they find. A server that says "PHP/7.4.3" in every response is volunteering for the list. A server that says nothing is skipped for an easier target. It also reveals when you are running software that is out of support, which is a bad look to anyone who checks, including prospective clients who run a scan before hiring a web company.
How to check
Our check reads the Server and X-Powered-By headers on your home page and reports any that include a version number. You can see them in a browser's developer tools under the Network tab.
How to fix it
On Apache, set "ServerTokens Prod" and "ServerSignature Off" in the server configuration, which your host may need to do. Turn off "expose_php" in the PHP settings to remove the X-Powered-By header, which many hosting panels offer as a switch. On Nginx set "server_tokens off". A content delivery network in front of the site usually replaces the Server header with its own.
Then do the thing that actually matters: keep the server software, PHP, WordPress and its plugins up to date, so that the version, hidden or not, has no known holes.
Not sure how your own site does on this? Run the free check: it takes about twenty seconds and reports on this and thirty other things.