We did a trial of M365 Copilot and our users found Copilot was very hit or miss when trying to edit existing slides including changing fonts (it was much better at generating new slides). I am hoping this gets better over time.
That one it can do but it is tricky. You have to open the template first and then delete the slide it has. Then tell Copilot to create a deck. Here is a good demo and further info: https://www.youtube.com/watch?v=RrM44aIlM2w&t=424s
