Hello @Elisay
The Release notes, mention the R2016a up to R2020a because, at the release date, the latest MATLAB version available is R2020a. From my experience, you can use the R2020b with no worries for the code generation, but there might be some issues with PIL, or may not. But for code generation, you can use the R2020b with no worries.
For not show any blocks in the Simulink Library Browser, just open the Simulink Library Browser and press the F5 button. If a dialog box appears, just use the option in the middle, smth with Generate in the memory, I can't provide a screenshot.
Regards,
Marius