I just stumbled across these on the internet and they are both great. These are for Keynote (on macs) but there are probably equivalent settings on Powerpoint.
1. If you want to be able to switch apps while in presentation mode (e.g. to see the Zoom window). Look at this guide on the Zoom documentation. There is also a setting where you can make your cursor visible at all times so you can use it to point at things on your slides.
2. If you want to play your slideshow in a window (so it doesn’t take up the whole screen). Go into this mode first, then share the keynote window from Zoom. (Downside: you won’t be able to see your “presenter view” from keynote, just the slides at they appear to others.