Export to PPT is missing on WORD online??

Yes. It is currently missing.

Microsoft seems to be experimenting/fiddling. It has appeared and disappeared a number of times over the years, including to the desktop application.

The thing is, although it was useful to you, apparently, it may have been misnamed or given others too high an expectation for what it would accomplish. I would expect that it will re-appear at some point.

Going to Outline View in Word and then copying and pasting may get you what you want, even though not as simple.

Note that I am a fellow user, not someone speaking for Microsoft.