filesystem navigation cannot follow junctions
On Windows 10 (and earlier Windows NT variants) it has long been possible to create "junctions" in a directory tree. These are the logical equivalent of a symbolic link to directory on Unix/Linux systems. Most programs are blissfully ignorant of the fact that a directory entry is actually a junction and will treat it just like a more integral part of the directory hierarchy. Meld version 3.20.0 will not follow them. (Interestingly, the earlier released version would.) Instead, in the file-open dialog, it acts as if they are not directories (showing no folder icon) and will "open" them if told to. (That is a useless "open", resulting in an apparently empty file.)
While trying to find a work-around, I found that Meld's file-open navigation is also unwilling to descend into a lettered drive listed in the left pane if it is the target of a subst mapping. (CLI shell command: subst X: \somepath... )
There is a semi-viable work-around. If Meld is started from a directory whose nominal path includes a junction, (making it the "current" directory), an icon for it will appear at the bottom of the file-open dialog left pane. From there downward, directories and files unreachable (by recent Meld) from the junction can be opened.
But of course it would be better if Meld could regain the pre-v3.20.0 behavior.