Thanks for the suggestion. We are evaluating it.Yuxiang [MSFT] commented
Thanks for your feedback Shogo, have you tried to create a PPT Online deck directly from the "Waffle" in the cloud storage portal, which locates on up-left corner and contains all the entry points of online application?
Click "PowerPoint Online", then you'll see lots of templates available there.
Please let me know if this works for you, looking forward to your feedback and more ideas! Thank you.