Hello,
First of all, thank you @RR123 for posting your experience here. Actually, you are right. There are a lot of staffs that impact on Google page speed mark that don’t depend on our theme. And anyway, you just need to read all the recommendation that you get in your page speed report and follow them if you want to increase the mark.
As we can see a lot of images are still not optimized https://gyazo.com/639234c4f1feb45bd0eb6c0b6565c6ce
Regards