CI says I need PHP 8.1

I'm trying to install CI, and when I view /public/index.php on my server, the screen reads:
"Your PHP version must be 8.1 or higher to run CodeIgniter. Current version: 8.0.24"
I thought CI is "intended for use with PHP 7.4+ (including 8.2)." (https://www.codeigniter.com/download)
What's going on? I'm unable to upgrade to PHP 8.1.

If I somehow manage to get an answer to my problem, how do I configure it so that the "/public" folder is not seen. Is that done with .htaccess in the public folder?

I'm thinking of going back to CodeIgniter 3 for this project. I never had such issue with it in the past. Would that be a mistake?

Merry Christmas!!