Not a game, but I was involved in making a graphics heavy app. Significant amount of times we had to grapple with question " that’s a nice feature you are making, will this work on all the platforms", and significant amount of times the answer was “obviously, unquestionably no”.
Unless you’re developing graphics-heavy application that uses platrofm-specific API for optimisation. Like a video game for example.
Are you talking from experience?
Not a game, but I was involved in making a graphics heavy app. Significant amount of times we had to grapple with question " that’s a nice feature you are making, will this work on all the platforms", and significant amount of times the answer was “obviously, unquestionably no”.
You should get some experience using modern game engines so you can see firsthand how easy it is to develop cross-platform games.
Supporting multiple platforms is a job for the engine developers.
And you should get some experience developing something more complicated than a simple unity project.