Hello,
thank you for reporting this issue. We're aware of the issue, but unfortunately we don't know the exact cause and we're are unable to replicate the issue on any our machine. We only know that Launcher see that dialog as if cancelled by user.

As a workaround, you can drag a folder with a mod from Windows Explorer to the list of the MODS page in Launcher.

Also I have made this little testing application: http://arma.jiripolasek.com/Files/selectfoldersdialogtest2.zip It's a test application that contains a multiple ways and combinations that open the dialog to see which combination won't work. The reporter that tried this application didn't tell us which option did or didn't work, but he reported that after click on all buttons and opening all dialogs, dialogs in Launcher started to work normally.

Hello,

Thank you for replying. I'm not exactly sure how the feedback system works, I hope you'll see my message here, because I don't know how to send a PM.

The workaround worked perfectly, thank you so much. This has made my experience unimaginably easier haha!

The application, however, did not. I made a separate folder, into which i extracted the .zip, however after starting I only see the windows spinning circle and the process (not as an application, only a process) is visible in the task manager, but it closes itself after a few seconds. Maybe it's related to the problem? If you need any log files from me, or anything, let me know, I'll be happy to help.

Hello,
the test application do nothing unless you click on the button (except of showing its window, of course), so there may be some connection. Could you open the Windows Event Viewer, navigate to Windows Logs / Application and look for any error that may be related to the test app?

I looked through the log files and I found the culprit - I had "Disable visual themes" and "Disable desktop composition" (desktop composition had no effect on this when enabled again) in the compatibility tab in the file properties of arma3.exe and arma3launcher.exe files (for increased performance - no Win Aero), but it's still weird, because I'm pretty sure that it really shouldn't cause this. When I enabled it again, mod selection started to work. I'll update the steps to reproduce to match. Thanks a ton, you guys are the best!

I can still paste the log files in case you want to read them.

Sir, you have my unending gratitude.

It's not the error we're looking for, but it's the bug I didn't even know about and thanks to you I now know about and it seems that I can make a workaround for this.

Also I'm still interested in those log files. Thank you.

The issue when a modern folder selection dialog is being unavailable due to modified compatibility settings has been resolved. As a workaround Launcher will detect that the dialog can't be opened and display an older version of the dialog if that is possible.

I still can't get the mod dialog selection going, and the workaround did not work either. I tried the testing app and everything displayed an "OK" when clicked.