If you want to use Unity3D - do yourself a favor - use a supported platform.
System requirements
OS: Windows 7 SP1+, 8, 10, 64-bit versions only; Mac OS X 10.12+; Ubuntu 16.04, 18.04, and CentOS 7.
GPU: Graphics card with DX10 (shader model 4.0) capabilities.
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If you really must use Manjaro - you are on your own - as unity3d is a custom package and custom packages are unsupported.