Theme Speed is Very Slow

I buy generatepress theme for my website and I know that this theme is very light and clean. And speed is very high. But whenever I install it on my website. In the Page Speed Insight it shows under 70 (link removed - not a buyer account).
Can anyone suggest me the solution. I dont want to change the theme. So any other solution is welcomed.

Use some cache plugins

My website speed is very much low even It could not pass the core web vital issue… Please suggest me some good way to increase the site speed that pass the core web vital scores.
I will be thankful to you

I can offer paid support if you’re interested in. You may need some theme modifications as well as server configuration.