I compiled my program in WIN64 and connected DB ..\examples\empbuild\EMPLOYEE.FDB with FB3 embedded x64, but I used Delphi XE10.2.3 ...
To have the exactly your error “[FireDAC]{Phys][FB]unavailable database” I must set : FDConnection.Params.Database := ''; Have you sure that property Database is not empty ? I you want, make a small demo with only a connection to a database and I will check if it works with DXE10.2.3 Eric