Instead of using TOpenDialog, Delphi provides super simple function can select directory as following:
uses Vcl.FileCtrl;
.
.
.
var
chosenDirectory : string;
begin
// Ask the user to select a required directory, starting with C:
if selectdirectory('Select a directory', 'C:\', chosenDirectory)
then ShowMessage('Chosen directory = '+chosenDirectory)
else ShowMessage('Directory selection aborted');
end;
Above is tested on Delphi 10.2