Thumbnails of images on the home page and empty space at the bottom of the site

Hello. I’m asking for help. How can I enable displaying thumbnail images on the home page instead of full size images? The problem is that it slows down my site and the homepage loading a lot. On most themes, the images in the small boxes are thumbnails.

Photo:
https://ibb.co/QvsyGFw
https://ibb.co/vJyMHWV

I have to stress that this is the best theme I have ever used. But it still needs some improvements and maintenance. Such as when I open a page with the sidebar off, a huge white space appears at the bottom of the site… Example: https://www.doxologiainfonews.com/2022/09/%D0%BF%D0%B0%D0%BF%D0%B0%D1%82%D0%B0%D1%83%D0%B5%D0%BE%D1%83%D0%B5%D0%B2%D0%B8%D1%82%D0%B5-%D0%BD%D0%B0-%D1%83%D1%80%D0%B0%D0%B3%D0%B0%D0%BD%D0%B0-%D1%84/

Photo: https://ibb.co/30CqtKX

Best wishes and blessings,
Alexander Angelov.

The page I need help with: [log in to see the link]