I attempted to do this today, as my first actual contribution to CPython itself.  I think the prior attempt went down a wrong path, which is why neither PR could actually pass tests.

I've been looking at `posixmodule.c` for comparison, specifically.  The key thing, I believe, is not to use `PyObject *filename` in the `dpmopen_impl()` calls at all, but rather `path_t *path`.  I tried some absolutely crude instrumentation to see why the `PyOS_FSPath` macro and the rest wasn't doing what it seems like it should (i.e. sticking `printf()`s in the .c files).  Eventually I realized that argument clinic is stopping me from even getting to the body of the function when `filename` was a PosixPath, so anything that PyOS_FSPath does is moot.

I think in the end the new code should be even simpler than the main (3.11) branch.  All I really need to do with a `path_t` is be able to call:

    PyObject *self = newgdbmobject(state, name, iflags, mode);

That is, `name` is simply the filename as char* (the other parameters are independent of the path-like issue).

Does anyone have pointers to an example or documentation about doing this? The patterns in posixmodule.c are suggestive, but I'm not sure of the missing pieces.

Also, I copied the typedef for path_t from posixmodule.c to both `_dbmmodule.c` and `_gdbmmodule.c`.  I know that's also going to be wrong, and it should be pulled into an .h file.  Any idea about which one? `posixmodule.h` seems like a possibility, but then I'd need to repeat it in `winreparse.h`.  Maybe a new name?