Last week I wrote about playing .pptx decks in the browser with their animations. To show how close it gets to PowerPoint, here are the same two decks in both, synced click by click.

What matches: slide layout and text, click-by-click entrance animations, and the morph between slides ending in the same place.
What differs: mid-morph, PowerPoint blends the color while the player rotates the shape first. Ordinary slide transitions fall back to a fade. It doesn't promise full PowerPoint compatibility, so test your own decks.
Everything runs client-side from a static folder. Full source included. One-time purchase.
https://207studio.dev/products/pptx-player-sdk/