Thanks, I found the problem! It appears both 7-zip and WinRAR on my PC was a bit too old, maybe the archive uses some newer compression algorithm. After updating them, the RAR-archive could be opened by both 7-zip and WinRAR. The itch.io app worked fine as well.
Now im off to listen to the "epic" version of the soundtrack, brb :)
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Glad to hear that! I think other people may find this thread helpful. And thank you for your contribution, it's very kind of you :)