upgrading to PHP 8 on slackware 15.0

I need to use PHP 8 on one of my servers. I see that there is PHP 8.1 in /extra so I thought I could just upgrade the default PHP to this version. Upgrade didn't work, so I removed the default php package and then installed the one in /extra/php81.

but it seems that it needs other packages to be upgraded as well. This is what I get from php --version:
Code:PHP Warning: PHP Startup: xmlrpc: Unable to initialize module
Module compiled with module API=20190902
PHP compiled with module API=20210902
These options need to match
in Unknown on line 0
PHP Warning: PHP Startup: apcu: Unable to initialize module
Module compiled with module API=20190902
PHP compiled with module API=20210902
These options need to match
in Unknown on line 0
PHP Warning: PHP Startup: imagick: Unable to initialize module
Module compiled with module API=20190902
PHP compiled with module API=20210902
These options need to match
in Unknown on line 0
PHP 8.1.20 (cli) (built: Jun 8 2023 15:41:52) (ZTS)
Copyright (c) The PHP Group
Zend Engine v4.1.20, Copyright (c) Zend Technologies
with Zend OPcache v8.1.20, Copyright (c), by Zend Technologiesand now httpd won't start either.

Has anyone used this package in /extra and if so, what should I be doing?

(I don't want to put this server on slackware-current)