Spasibo Dima, I used TFDQuery with

EXECUTE BLOCK AS
DECLARE VARIABLE stmt VARCHAR(1000);
BEGIN
for select 'ALTER INDEX '||rdb$index_name ||' ACTIVE;'
from rdb$indices
where (rdb$system_flag is null or rdb$system_flag = 0)
order by rdb$foreign_key nulls first
into :stmt
do EXECUTE STATEMENT :stmt;
END

I call it

  procedure ActivateAllIndexes(dbConn: TFDConnection);
  begin
    dbConn.StartTransaction;
    try
      FDQuery1.ConnectionName := dbConn.ConnectionName;
      FDQuery1.ExecSQL;
      dbConn.Commit;
      ShowMessage((Sender As TButton).Caption + ' executed successfully for ' + dbConn.ConnectionName);
    except
      dbConn.Rollback;
      ShowMessage((Sender As TButton).Caption + ' failed for ' + dbConn.ConnectionName);
    end;
  end;

It works like a charm!  No issues! Esche raz Spasibo!