I hope you are well today and thank you for your question.
To troubleshoot the issue, could you please try clearing and temporarily disabling the WP Rocket cache plugin?
To add search form to the menu, you have to use the below plugin.
Yes, the Gillion theme applies a lightbox effect on the featured image as shown in the below page.
now it’s work with other plugin,
Glad it’s working for you.
it’s not possible to put search icon at top menu or main menu?
You can try achieving this using the below plugin or contact the plugin support to achieve this.