Disclaimer: Don't mess with your system if you do not know what you are doing.
This is a mere little hack to sparkle a discussion aboit adding a non transparent theming option for SailfishOS to speed up things for older SailfishOS devices.
The patch (that cannot be applied ootb because of different filenames) disables transparency for lipstick and most of the apps. Its meant as a reference and maybe I missed some points where transparency can be disabled.
Feel free to add some more places if necessary.
You can find it here: https://llelectronics.neptuneos.com/s/sbAwMZPZMMceKqN