To resolve most of the recent errors and FPS issues, please manually update your windows to version 1903. To run properly, League requires you to have the latest windows update installed and major windows updates like these aren't often automatically updated. This is quite large update, so it may take awhile to do. (1-2 hours). The longer you wait with this, the more issues your're going to have. Once update has been installed, restart your computer.
Once windows has updated to ver.1903, manually search for updates again and update your .NET frameworks!
NOTE: A simple windows update fixed my issues, there can be multiple other reasons for you to have issues.
Thank you for your attention and gl/hf :)