Good read, and I think you might want to look at OnlyOffice. It’s open source and while it is kindof a shameless Microsoft Office clone, it does seem to support LaTeX when adding equations. Not sure how well it works as I don’t use it though. The slides app is pretty decent, the only bone I have to pick with it is that there aren’t many animation types and most of them are very basic. Otherwise, might be what you’re looking for.

Edit: I just tried it and it seems to work pretty well. Select LaTeX, type your equation, then select professional in the dropdown menu and it’ll show the equation.