I am trying to download an old version of Gecko SDK through the Package Manager in Simplicity but all the buttons are grayed-out (see the attached pic). How can I download the correct files? Under the category "32 bit MCU" one can also download other versions of Gecko SDK but not older than v4.4.0 (see attached pic 2).
There are two different Gecko SDK products. The "Gecko Platform" refers to the unified platform, that combined the various Wireless Protocols (Bluetooth, Zigbee (EmberZNet), Flex, etc) along with the 32-bit MCU SDK (EFM32 support). All of the protocol and MCU SDKs are built on top of and share the common Gecko Platform. Since the SDKs depend on (require) the Gecko Platform, the corresponding Gecko Platform version is automatically installed the first time one of the corresponding Wireless SDKs or MCU SDK is installed. The older name for the 32-bit MCU SDK was the "Gecko SDK" and it only included the 32-bit MCU support. This was the name used before the code was refactored and the "Gecko Platform" was created. The oldest "Gecko SDK" that Simplicity Studio supports is version 4.4.0 as you have indicated in your post and screenshots.
To install Gecko Platform version 2.2 you would install 32-bit MCU SDK version 22.214.171.124. If you expand the release notes you can see that it mentions it requires "Common Platform" version 2.2.0.
Sorry for the confusion in terminology, I hope this explanation helps.