Same problem with Keynote - Mac-only, hard to convert to PDF if you don't have Mac, or you don't want to send a private deck to a conversion service.
Then briefly I used Prezi for public stuff.
I used reveal.js for teaching course with lots of code snippets. There are many similar markdown or other text-based presentation frameworks, some come with associated services, if you don't want to host them by yourself.
Now I use mostly Google Slides - it's the most portable solution (even mobile and iPad). It doesn't work offline, but I make sure to have a builtin 4G modem in my laptop and iPad. For the important presentations I always export slides as a PDF for backup.
For good looking slides with minimal effort: beautiful.ai
On their site they have a comparison to other solutions:
PowerPoint
Google Slides
Keynote
Prezi
Slidebean
Visme