Sorry I misunderstood. It didn't occur to me that you were building an appliance (I'm not sure why after all the updates you did for v18.0!).

So please ignore my note re that script. In appliance build code, you'll need to do a couple of things:

Makefile:

Add this line:

PHP_VERSION=8.1

If you want/need any other packages from the repo other than ones that start with 'php' or the Apache module, then they can be auto pinned (security) at build time by adding them as a space separated list to the PHP_EXTRA_PINS env var in the Makefile. E.g.:

PHP_EXTRA_PINS=package1 package2

Plan:

Replace the line that includes the lamp plan, with lamp81. I.e.:

include $(FAB_PATH)/common/mk/turnkey/lamp81

And all the php module packages you include in the appliance plan need to include the version. E.g.:

php8.1-cli
php8.1-curl
php8.1-json
php8.1-zip
php8.1-mbstring

Etc.

There is at least one exception. The only one I can think of that doesn't want the version is php-pear, although there may be others. If you get a package not found at build time for a package that includes 8.1 in the name, try removing the version number.

Good luck and ask if you have more questions and let me know how you go. I'm also have a look at your code if you push it to GitHub.

FYI, as is likely clear, the PHP version can be changed to any PHP versions provided by sury.org - scroll down and look for directories that start with phpX.Y. Although it will also need an associated version plan in common.

Also note that only PHP versions supported by upstream are guaranteed security updates - although I know that if sec updates are available for old, unsupported versions, the maintainer of DEB.SURY.ORG will apply them when possible. It's also important to be aware that non Debian PHP versions aren't auto updated and will required regular manual update.