Testing configurations in order to find the "Minimum" requirement for Arma Reforger based on not too old hardware parts, I am getting this error message.
The tested GPU is a GTX 750 Ti based upon Maxwell and supporting DX 12.
This GPU although DX12 compatible is considered too weak to play Arma Reforger and is excluded from the Database resource, this must be explicitly mentioned.
It may be necessary to add that 4 GB of Video Ram is mandatory if it's the case.
Edit 02/06/2022 : Arma Reforger is running on an AMD RX 550 2 GB, so it's only a case of Database resource update.