How do i insert a PPT slide(s) into a Final Cut Pro video?

Try either of these:

Save a single slide as an image

1. In Normal view, open the slide you want to save.
2. On the File menu, select Export.
3. Under File Format, select the image format you want (JPEG, TIFF, PNG, or BMP).
4. Select Save Current Slide Only. You may also enter a size for your slide image in the Width and Height boxes.
5. Select Export.

Exporting your PPT as a movie

https://support.microsoft.com/en-gb/office/turn-your-presentation-into-a-video-c140551f-cb37-4818-b5d4-3e30815c3e83#:~:text=Select%20File%20%3E%20Export%20%3E%20Create%20a,the%20larger%20the%20file%20size.

You can export slides as separate images and use them like you would use any other images.

If you want not just stills but animation you can export a Quicktime movie right from PPT and then use that for further editing in FCP.

FWIW, I prefer Keynote, but you can do this sort of thing easily with either of these applications.