[How we can design a fliter in wordpress for ecommerce website]

Try to use 'WooCommerce AJAX Products Filter' by Berocket
https://berocket.com/woocommerce-ajax-products-filter?utm_source=paid_plugin&utm_medium=plugins&utm_campaign=ajax_filters

[How to fix elementor issues?]

Set your hosting PHP version 7.4 
update elementor . elementor plugin with the latest version.

[Wordpress Japanese spam removal]

To remove spam, and malware attacks, the Wordfence plugin is the best solution. 

[How to fix this error? Wordpress]

1. Deactive all of your plugins
First, log in to Cpanel and then remove all plugins (create a backup first)

2. then try to refresh the login page (Hope it will be fixed)

3. At last activate all the plugins one by one and check again if it's a conflict or not.