In a composited environment, fullscreen windows are just maximized windows without a border, which triggers some heuristic to unredirect windows (i.e. does not have to pay the price of compositing) when they are the sole thing that is drawn on the screen.
So, on Linux, fullscreen and maximized borderless are the same. Given that Windows is a fully compositing desktop as well, I wonder why the difference still exists.
Some legacy apps (that is, games) react very badly when they're not in full control of their window sizing, priority, input and device polling, ecc.
The current day approach is to instead do the "large borderless window" and then do software scaling of the image in order to match the display resolution. One cool result of this is you can get much better scaling than your display would do naively. Low-res games really benefit from software integer scaling instead of "whatever scaling the display firmware does, usually making all the edges blurry".
Rescaling in software is so fast now that some graphically intense games can do per-frame scaling in order to keep per-frame latencies below a particular goal threshold, at the cost of your game losing fidelity (getting blurier). It's so common that most big-name titles now do this.
> The modern strategy is to just do borderless windowed and pretend true fullscreen doesn't exist.
This explains a lot as to why I experienced some interesting inconsistency going full screen in different applications in Windows ;)