I need to increase the units per Em from 1000 to at least 2000 in order to get a higher level of detail for small curves and round corners.
How does the increase in grid units affect the export of otf and variable fonts?
Could it create conflicts in specific softwares, browsers or other applications such as Adobe, Figma etc.?
The export will be fine. If you go further (3000–4000), you might run into problems: InDesign + dlig error
in my experiments in that thread, I could make a glyph 3500 units wide without consequence. anything above that was a mess.
Yes. Or you use fractional coordinates.
So is there even any advantage in increasing the EM, when you could just use fractional coordinates?
it is a bit easier to get consistent drawings when you have any grid.
How do they work? I’ve never heard of them
You can set a grid smaller then 1. E.g. by setting the grid to zero or by increasing the subdivision. When exporting as CFF, those fractions are exported.