By default, the Filter Everything plugin is configured to work optimally on most sites. However, this does not mean that this configuration will be the best in your particular case. For example, for security reasons, the AJAX query feature is disabled by default. You will probably want to use it.
To enable the AJAX feature in the WordPress admin panel go to the Filters > Settings menu and activate this function with the appropriate checkbox. Save changes and try to check if AJAX is working properly.
If you have problems, try to specify the “CSS ID or Class of Posts Container” in appropriate field on the Settings tab, where you enabled AJAX. With a high probability your theme is different from WordPress standards and contains an unusual posts container.
Most filter widget elements inherit styles of your current theme and therefore should look harmonious on your site. However, you can make your filters more appropriate with your site design by specifying the primary color of the Filters widget elements. To do this, go to Filters > Settings and specify a color that matches the color scheme of your theme in the Widget Primary Color setting.