This was originally discussed on the a11y mailing list:
https://listarchives.libreoffice.org/global/accessibility/msg01259.html

Steps to reproduce on Windows:

1) start NVDA screen reader
2) start Impress
3) make sure "View" -> "Slide Pane" is enabled
4) create a few slides using Ctrl+M (or alternatively open a presentation that has more than just 1 slide)
5) press F6 until focus is in the slides pane
6) press Tab to move focus to a slide in the slides pane
7) use Up/Down keys to switch between slides

Actual result:
NVDA doesn't announce the newly selected/focused slide in the slides view.

Expected result:
NVDA should announce the newly selected/focused slide.

Additional information:
NVDA 2025.1.2

With a current NVDA development version, this exception can be seen in NVDA log:

ERROR - eventHandler.executeEvent (13:46:32.234) - MainThread (10300):
error executing event: gainFocus on <NVDAObjects.IAccessible.IAccessible object at 0x0AEBDFF0> with extra args of {}
Traceback (most recent call last):
  File "eventHandler.py", line 348, in executeEvent
    if isGainFocus and not doPreGainFocus(obj, sleepMode=sleepMode):
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "eventHandler.py", line 382, in doPreGainFocus
    if not api.setFocusObject(obj):
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "api.py", line 189, in setFocusObject
    setNavigatorObject(obj, isFocus=True)
  File "api.py", line 348, in setNavigatorObject
    review.setCurrentMode("document", False)
  File "review.py", line 140, in setCurrentMode
    pos = func(obj)
          ^^^^^^^^^
  File "review.py", line 59, in getDocumentPosition
    pos = obj.treeInterceptor.makeTextInfo(obj)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "documentBase.py", line 76, in makeTextInfo
    return self.TextInfo(self, position)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "compoundDocuments.py", line 287, in __init__
    self._start = self._end = self._startObj.makeTextInfo(position)
                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "documentBase.py", line 76, in makeTextInfo
    return self.TextInfo(self, position)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "textInfos\offsets.py", line 505, in __init__
    self._startOffset = self._endOffset = self._getCaretOffset()
                                          ^^^^^^^^^^^^^^^^^^^^^^
  File "textInfos\offsets.py", line 267, in _getCaretOffset
    raise NotImplementedError
NotImplementedError


Version: 26.2.0.0.alpha0+ (X86_64) / LibreOffice Community
Build ID: 19fa16859e65ebdf86554110cecbecf67e9594e1
CPU threads: 12; OS: Windows 11 X86_64 (build 26100); UI render: Skia/Raster; VCL: win
Locale: en-US (en_DE); UI: en-US
Calc: threaded

(which is master as of bc58a54d513702bc07906627dce073f05d7978fd + 2 unrelated pending Gerrit changes, see https://gerrit.libreoffice.org/c/core/+/187183/2