Hi @catalintpopa,
Please do note that Mobile in general will have a lower score compared to Desktop as the display size is smaller. It entirely depends upon the capability of the theme how much it can be optimized without breaking the theme layout, as the changes will also affect the Desktop.
When I check the website via Google Page Speed, the primary factor for a low score in Moblie seems to point to “Reduce initial server response time”. Enabling Server-side cache should help with such cases. Bringing this to your Hosting provider attention would help.
For the rest of the files listed in Google Page Speed ie for Unused CSS and render-blocking issues, I don’t see much of an improvement that could be done, as the plugin has already optimized the files to it’s optimal. However, if you haven’t tried the “Manual” mode in Asset Optimization, would recommend giving that a try and see whether it helps, however, it won’t bring any significant improvement as the files are already optimized.
For Preload Key request, you can try the method mentioned in the following article to improve Preload key request for the respective files listed in the Google Page Speed result:
https://www.stramaxon.com/2020/02/preload-key-requests-wordpress.html
The code can be implemented as a mu-plugins. Please check this link on how to implement the above code as a mu-plugins:
https://premium.wpmudev.org/docs/using-wordpress/installing-wordpress-plugins/#installing-mu-plugins
Kind Regards,
Nithin