Compatible side by side NDK version was not found

Go to SDK manager => Appearance and Behavious => System Settings => Android SDK => and install NDK side by side.

It could be tricky to find the compatible version with your application. For android API level 29, version 20.1.5948944 worked. So, if you are trying some older API level you should try some older version.

When the version of NDK side by side is not compatible with your application needs then following errors may occur:

No toolchains found in the NDK toolchains folder for ABI with prefix: arm-linux-androideabi

Or

No toolchains found in the NDK toolchains folder for ABI with prefix: llvm

Thanks and Cheers !!!