uncached JavaScript and CSS files

hello I am doing seo with SEMrush and I got this message about the plugin :

142 issues with uncached JavaScript and CSS files

https://prnt.sc/N9gYMkcYfn0z

also the site is on your server if it is metter.
please help me to solve this or figure it up.

thanks
Roey