Dear Drupal friends. 2 months ago I installed Drupal and it has been 2 months lost. I have not advanced anything. the current configuration is that of the first day. Every time I try a change it is damaged. Every time I try to install a new theme, it gets damaged. The themes used, say they are compatible with Drupal 8.4.4. The front of the page, shows the following: The website encountered an unexpected error. Try it again later </br></br><em class="placeholder">InvalidArgumentException</em>: Field is unknown. in <em class="placeholder">DrupalCoreEntityContentEntityBase->getTranslatedField()</em> (line <em class="placeholder">509</em> of <em class="placeholder">core/lib/Drupal/Core/Entity/ContentEntityBase.php</em>).
Again I have to restore the backup, again and again.
Why can not I install the themes? neither by file, nor by composer