Again, I will not here that Notepad++ is a Windows application, and the developers only support Windows environments; if you can make it work in Wine (which is what PlayOnLinux uses under the hood), great for you! But that’s not a supported use case.
2 Notepad updates prior to v8.1.4 (32-bit) on Ubuntu 18 with PlayOnLinux disappeared the option to go Up to upper folders. This is very uncomfortable. Please put it back. Thanks.
The Notepad++ Open File dialog does allow going up directories, in the same way it always has. If Wine/PlayOnLinux do not support the standard windows API calls that Notepad++ uses to get the OpenFIle dialog working, then the problem is with Wine/PlayOnLinux, not with Notepad++.
Sorry.