I used to rank in top 3 for several keywords. But now they are in position 8-10 after change my theme to Generatepress.
After checking with Ubersuggest, I found all my pages doesnt have H1 Heading.
your site is built with Elementor and the Elementor Full Width template which replaces the themes templates. Changing to GP would have had no effect on this.
I checked most of your pages and all of them have a H1 that is added in your elementor pages.