my %file_system = (
 '/path/subpath1/'=>['file1', 'file2', 'file3'],
 '/path/=>['fil01', 'fil02', 'fil03', 'fil04', 'fil05'],
 '/'=>['f001', 'f002']
);

my $cpath = '';

my @folders = sort keys %file_system;

for my $folder (@folders){
 print "$file_system{$folder}\n"; #Everythng is ok. Prints an array refernce, such as: ARRAY(0x3381e118)
 print join(';', @{$file_system{$folder}}), "\n"; #Everythng is ok. Prints an array
}

my $listFolders = $win->BrowseEntry(
 -label=>'Folder:',
 -choices=>[@folders], #Also tried \@folders, and also, omitting -choices parameter, used $listFolders->insert('end', @folders)
 -variable=>\$cpath,
 -browsecmd=>\&listFiles();
)->pack(
 -side=>'top',
 -anchor=>'nw',
 -fill=>'x',
 -expand=>1
);

#Testing $cpath, after selection:
print "$file_system{$cpath}\n"; #Sometimes prints an array refernce, such as: ARRAY(0x3381e118), sometimes not, even, though, visually, the $cpath looks the same as the according path in the %fule_system var
print join(';', @{$file_system{$folder}}), "\n"; #Sometime prints an array, sometimes an array is NULL.

#If I iterate keys %file_system, I see the path, that's in $cpath var, but for some reason, it doesn't match.

#Testing $cpath inside the function called from the Tk widget:
sub listFiles{
 print "$file_system{$cpath}\n"; #Sometimes prints an array refernce, such as: ARRAY(0x3381e118), sometimes not, even, though, visually, the $cpath looks the same as the according path in the %fule_system var
 print join(';', @{$file_system{$folder}}), "\n"; #Sometime prints an array, sometimes an array is NULL.
}