Beware:
Upgrading to 9.4.0 on Joomla 3.10.12 cause errors when you try to manage users.

0 Non-static method Joomla\CMS\Application\WebApplication::getBody() cannot be called statically

I have tracked out its due to an issue when Joomla Integration plugin is enabled.
I am awaiting response from support team.

Alan

I already replied in your ticket, but since you also opened a warning here, let me reply also here

I have tried to create new subscriber on my test installation from both frontend and backend and I couldn't replicate the issue

This problem seems to be specific to your environment. That is why I have asked for the access details, so our developers can debug this on your installation and see what is going on