@IKS the solution I proposed worked!
I did some tests and putting a MicroSD type A1 the system is much more stable, faster and I was able to install the Playstore.
"System Optimization" disappeared at the second start and did not appear anymore.
The Playstore is very stable, except when you need to install apps. I suggest direct installation from the search menu instead of selecting the application and installing it from there.
I attach links for reference on which model I have purchased:
https://www.amazon.it/gp/product/B06XYT37NK/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1
I would like to know whether other people have solved the problem with this solution.