Hello, @Tamara,
1- I have checked your site on my personal mobile and found no issue. The category filter button works just fine also the mobile menu category dropdown works perfectly. Please watch the video for a better reference and then check back to your site after clearing the browser cache: https://streamable.com/om9vix
2- I have checked your site speed score it is low. Check the image I have underlined the cause of the speed: https://postimg.cc/bs8P6jh3 You need to optimize the cache and JS code so that the server response time will auto optimize and word fast. By doing this your site speed score will be enough. You can use the WP Rocket plugin for this check this article for more information:https://xstore.helpscoutdocs.com/article/128-how-to-improve-wp-rocket-settings-with-xstore
Regards 8Themes Team.