I'm a bit late to the party, but I finally took some time to properly test this beauty. Here's what I found:

After starting the BMM 1.16.1 I get the following line in the terminal running Wine: "wine: Read access denied for device L"\\??\\Z:\\", FS volume label and serial are not available."

Does not close on "X" any more, has to be force quitted. Can't replicate that now, probably just bad luck the first time around.

Profiles are saved, but not automatically shown when going back to "Manage profiles..." but rather have to be reimported via "Load file...". This works, however after pressing "Use" I get that same "wine: Read access denied for device L"\\??\\Z:\\".

Automatically extracting .7z files works properly and even shows the elapsed time. The last digit of the seconds is cut at the midpoint but doesn't really matter.

"Increase priority" and "Decreade priority" have no arrows, but just rectangles (see screenies). Other than that they work as intended.

About page works with link and licence.

"Install mod archive(s)" and selecting a .7z file in the DMM folder brings a tiny popup (see screenie). After pressing Enter I can choose the .7z file again. Then comes a bigger popup (see screenie), telling me I am stoopid. Also cut off a tiny bit in the end. Also it's "Cancel" (or "Abbrechen" in your case) and not "Abort". You might want to add to the message, that the user could reopen the modmanager to extract these mods automatically (since it always does that just on the startup, not when you copy mods in there with it already running). Suggestion:
Code:
Do not select archives from the DMM (mods) folder.
They are installed automatically.
Simply restart the Mod Manager
or select an archive from a different folder.
"Install mod archive(s)..." works properly when selecting from a different folder (as is intended).

"Delete" and pressing Del/Entf on the keyboard both work as intended. Popup cut off though. Sometimes the popup is tiny, similar to the other tiny popup. Can only press enter (which closes since "Yes" is preselected),  also when it's tiny like that. Can't resize. Alt+N (No) or Alt+Y (Yes) work though.

"Lookup mod (WWW)" works as intended.

"Open ReadMe file" works as intended, very nice addition!

"Open mods folder" opens the mod folder in a Wine window (and not the installed file manager, Nemo in my case) and is ugly af. Don't care tho, since most people know how to navigate to the DMM folder anyway.

"Select game folder..." seems to work well and finds SS2.

Duplicate folder name warning works, you good, good man!

Drag'n'drop does not work.

Ctrl+S saving works.

Button is called "Launch game", not "Exit and start game" as the releasenotes in Github say. I vaguely remember there being a discussion to rename the button to something else or whatnot. I preferred the "Exit and start game" but it doesn't really matter. It does what it's supposed to do.

Wine build: 5.0

Anything else you'd like me to look into?
[InstallModArchives_popup.png expired]
[DMM_folder_popup.png expired]
[DeleteMod_popup.png expired]

I should be getting back to this just about... now soon.

@JML
* Concerning read denied warnings: Do you just get a warning in the console or are there actual problems with the functionality? I'm just using basic wxWidgets file system functionality, reduced to the limited NTFS feature set of Wine. No changes at all since the project started, so no idea what I could do to fix.
* Saved profiles not shown immediately: This is intended. However, the use button should have stayed disabled. Fixed
* Cut-off deletion sentence: Probably one of a couple of million different things that can go wrong with string manipulation between operating systems.
* Missing symbols: Wine issue with Unicode symbols and Windows BOM. I tried several ways to implement Unicode symbols, this is the only one that worked consistently on Windows. Shame about Wine.
* Cut-off popup: Does the terminal tell you anything interesting when that happens? The deletion dialog is the same as any other standard dialog. Does this always happen with a certain mod folder, maybe containing invalid characters?
* Drag and drop: Shame. The feature relies on certain refresh timings working correctly. Win only then. Thanks for the feedback!
* Wording: Where exactly does it still say "Exit and start game" anymore? I thought I changed that everywhere.

@voodoo47 Added *.nut file support to most recent version.

Edit: Wait, no. Are .nut files always in a subfolder? Only checking main folder so far.
//FIXED!

Continuing here: https://www.systemshock.org/index.php?wap2;topic=4790.0