I use Delphi 10.4.2. I downloaded the examples.fdb ( 3.0 ) directly for Firebird.org.
When I click on Test I instantly get a [FireDAC][Phys][FB]connection rejected by remote interface.
I am stuck. The Delphi website says you are probably connecting to FB Server with FB Driver using GDS32.DLL.
I needed to download the Firebird 2.5 Embedded driver. After this in Delphi I configured FDConnection as above. I also dropped an FDPhysFBDriverLink1 on the form. Here I checked Embedded and set the Vendorlib to the fbembeded.dll. And it works.