Admin area errors in Joomle 4, with standard...

When I rename htaccess.txt to .htaccess, the following fatal error appears in my Joomla 4 admin area. (Using the Joomla 3 .htaccess works OK.)

An error has occurred.
0 syntax error, unexpected '|', expecting variable (T_VARIABLE)
Call stack
# Function Location
1 () JROOT/libraries/regularlabs/src/Parameters.php:23
2 Composer\Autoload\includeFile() JROOT/libraries/vendor/composer/ClassLoader.php:428
3 Composer\Autoload\ClassLoader->loadClass() JROOT/libraries/src/Autoload/ClassLoader.php:59
4 Joomla\CMS\Autoload\ClassLoader->loadClass()
5 spl_autoload_call()
6 class_exists() JROOT/plugins/system/advancedmodules/advancedmodules.php:28
7 require_once() JROOT/libraries/src/Extension/ExtensionManagerTrait.php:217
8 Joomla\CMS\Application\CMSApplication->loadPluginFromFilesystem() JROOT/libraries/src/Extension/ExtensionManagerTrait.php:160
9 Joomla\CMS\Application\CMSApplication->loadExtension() JROOT/libraries/src/Extension/ExtensionManagerTrait.php:99
10 Joomla\CMS\Application\CMSApplication->bootPlugin() JROOT/libraries/src/Plugin/PluginHelper.php:232
11 Joomla\CMS\Plugin\PluginHelper::import() JROOT/libraries/src/Plugin/PluginHelper.php:192
12 Joomla\CMS\Plugin\PluginHelper::importPlugin() JROOT/libraries/src/Application/CMSApplication.php:744
13 Joomla\CMS\Application\CMSApplication->initialiseApp() JROOT/libraries/src/Application/AdministratorApplication.php:312
14 Joomla\CMS\Application\AdministratorApplication->initialiseApp() JROOT/libraries/src/Application/AdministratorApplication.php:165
15 Joomla\CMS\Application\AdministratorApplication->doExecute() JROOT/libraries/src/Application/CMSApplication.php:293
16 Joomla\CMS\Application\CMSApplication->execute() JROOT/administrator/includes/app.php:61
17 require_once() JROOT/administrator/index.php:32

I'm hosting Joomla 4.4.3 on Siteground with PHP 8.1.27, latest RegularLabs plugins.

Any ideas?

thanks,
Geoff

Yes, I did the "Update All" after the upgrade, but just to be sure, I've again individually "reinstalled" each one just now, but still getting the same error.

Installed
Extension Type Version
Advanced Module Manager Component Action Log Plugin System Plugin 10.0.21 PRO
Cache Cleaner Module System Plugin 9.1.0
Conditional Content System Plugin Editor Button Plugin 5.1.5
Regular Labs Extension Manager Component Action Log Plugin 9.0.0
GeoIP System Plugin Library 6.0.4
Modals System Plugin 14.0.11 PRO
Modules Anywhere System Plugin Editor Button Plugin 8.1.1 PRO
Sourcerer System Plugin Editor Button Plugin 10.1.1

Would you like me to post it here? BTW - I have reinstalled the core Joomla files, and using PHP 8.1.27 and MySQL 5.1.4

Thanks Peter, I've followed your instructions, and things seem OK now. Much appreciated!