It's not easy, but I've installed Firebird-4.0.2.2816-0-x64 and Firebird_ODBC_2.0.5.156_x64, and performing a simple query which displays the records in employee table.
I managed to get TestComplete to also connect, and also display the employee records.
TC 64-bit can interact with 32-bit applications. If your app is 32-bit, then your ODBC driver also needs to be 32-bit.
What is the connection string you have used
I am using connection string as
Qry.ConnectionString ="DRIVER=Firebird/InterBase(r) driver;UID=SYSDBA;PWD=******;DBNAME=C:\\FireBird\\400-Environment\\400-Environment\\2.34\\DbFirebird\\Test.fdb;READONLY=YES";
