PHP 8.3 is the newest php-Version: PHP: Supported Versions
Nextcloud 28 supports php8.3. Unfortunately, a lot of apps donât yet. The result would be that these apps will not be updated or offered for installation unless they have also been updated to php8.3. For that reason, it is recommended to stick with php8.2 for now. However, if you know your way around, you can install php8.3
With the commandline app store nc-apps it is possible to run Nextcloud under php8.3 and still browse all available apps, even when not compatile with php8.3 and bring the php8.2 apps up to date if a php8.2 minimal-installation beside your php8.3 is present.
Much and good luck,
ernolf