Hello. I have a problem with adding and editing an existing user. The following error is displayed:
Call to undefined method Joomla\CMS\Application\AdministratorApplication::isAdmin()
Link to the movie: https://www.mck.skarzysko.pl/images/joomshaper_forum/Ekran.mp4
This message is also displayed on the home page:

I found this to be a problem with the AcyMailing component.

After uninstalling the component, I can edit and add Users, but uninstalling resulted in more errors.
After reinstalling, the errors do not disappear.


The website has just been installed. Any suggestions to fix the problem.
Regards, Michał