Hello. No -there is no import powerpoint option in the Lesson activity; you are correct. (There was, many years ago, but it stopped working with modern Power Point and was removed) If your PPT slides don't have animations, then you can save them as images such as png (one of the save options in PPT) and then upload them to Lesson content pages as embedded images.
(Or you could use a external site such as Slideshare and add your PPT there and embed it in to a page or label, but then you won't get scoring if you want the Lesson in the gradebook.)
Another possibility is to transfer the PPT content by hand to the lesson, one slide at a time to a content page or question page, as needed. A lot of duplicate work, but worth it in the end. I did a few myself, but generally would have students do them for me, as bonus work.
Once I got them all into Moodle, I quit using PPT, and just made all my "slide shows" in Moodle. Of course not using PPT means you have to give up a lot of the gee-wheeze animations and stuff, but it is amazing what you can do by using Justin Hunt's Generico filter and other widgets.
