After restarting Apache and running PageSpeed again I got 93/100 for Desktop Optimization!
After updating Sucuri plugin I also noticed one new security recommendation: Disable Server Banners. Essentially they recommend to turn off any information exposing your server version and modules. For that I just added two lines to /etc/httpd/conf/httpd.conf:
ServerSignature Off ServerTokens Prod
And the last minor note that I had no issues with upgrading my AWS instance to Amazon Linux 2018.3. And they actually help you to do that in motd:
sudo yum clean all sudo yum update
And you will get latest Linux 4.14 kernel and bunch of updates. I encountered no issues with my WordPress after restarting my box.