Hello,
All the options that are available in our theme for the optimization you can find in Theme Options > Speed Optimization. We don’t have any other extra settings at this moment.
Our team is working on JS optimization and general theme optimization, this task in the process https://www.8theme.com/roadmap/ , so can’t give you any theme update at this moment.
Check the recommendations from this post https://wp-rocket.me/blog/how-to-reduce-ttfb-wordpress-site/ Maybe you’ll find something useful for you.
Besides, when we test your site using GTMetrix TTFB is 0.6 https://gtmetrix.com/reports/s-marina.se/AoEYRTZR
Regards