We currently set the default PHP (latest and plain tags) to be one that is supported upstream, but at the same time, we could be a catalyst for pushing a PHP version out of "beta support" in WordPress. Unfortunately, I don't know of a good non-subjective line for when to swap the default PHP to one of the "beta support" PHP releases in order to help push it out of beta.

https://make.wordpress.org/core/2025/04/09/php-8-support-clarification/

Usage of PHP 8.3 and higher is at 8.9% of all WordPress sites as of April 2025. Once this surpasses 10% and assuming no further compatibility issues are reported then it’s expected that the beta label for PHP 8.3 support will be removed in the subsequent major release of WordPress