Hello and welcome to our forum,
I noticed that in the Advanced Installer, when I click the 'Configure' option, it opens the 'BrowseDlg' dialog where I can choose the installation location. However, when I compile the 'App Installer' theme, the 'Configure' option doesn't work, and when I click it, the installation starts immediately without showing the 'BrowseDlg' dialog where I can choose the installation location.
This is because by default no other dialogs are added. You must add the FolderDlg dialog manually or any other dialog.
Right click on the
WelcomeDlg →
Add Dialog →
FolderDlg.

- folderdlg appinstaller.png (107.88 KiB) Viewed 9089 times
I need to drag button (1) to the left to see button (2), which is also hidden (4). I need to select 'Visible' and bring it to the front (3) to see button (2).
You can easily select hidden controls from the drop-down option in the Properties right pane:

- properties dialog.png (97.35 KiB) Viewed 9089 times
Let me know if you have any questions.
Best regards,
Liviu