You cant cache third party images but if you install plugins to download and cache, maybe that could be a solution ( Check this web: https://bateriaselectronicas2000.com/ ). Anyway, there is no problem about SEO, your gtmetrix report 81% / 70 % is good enought.
It has happened to me with the latest version on this website
https://busturistico.info/, but I have returned to the previous version and it works perfectly.
