You need to wait for 3.10.X to become available; as per the documentation, "This guide assumes you are starting on Joomla 3.10.x. If you are on a earlier version make sure you upgrade to Joomla 3.10 first before moving to Joomla 4." Joomla 3.10 is currently in development, at 86% completion, most notably, with no completion date for release. V3.10-...


This should still work in 4.0 but will break in 5.0. You are advised to use fully qualified class names. Remove JLoader::register() call and instead add a use statement: use Joomla\Component\Fields\Administrator\Helper\FieldsHelper;


Just an FYI that Joomla 3.10-alpha has now been released so the upgrade process can now easily done. Instructions: Go to the Joomla Update Component Options and switch the Update Channel to Testing and the Minimum Stability option to Alpha. Update to 3.10 alpha1 using the Joomla Update Component. After you have updated to 3.10 alpha please switch the Update ...

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