Display configuration: Mac, single display, 1440 × 900, dock visible on bottom. Steps to reproduce:

1. In the launcher profile settings, specify a resolution vertically larger than the maximum window size that fits on the screen.
2. Launch Minecraft.
3. Observe that the window fits on the screen, but the content (both GUI and 3D viewport) is sized according to the launcher settings and therefore cut off at the top.

This is useless and otherwise impossible behavior — the resolution setting is otherwise equivalent to resizing the window, but resizing the window will not create this clipped-at-the-top behavior. I think it would make sense for Minecraft to, after setting its window size, check what window size has been actually achieved and adjust its notion of resolution to fit that.

My goal is (rather, was at the time I reported this bug) to have Minecraft in a maximum-size window. It is not trivial to work around this problem simply by specifying the “correct” size, because on macOS the maximum vertical window size varies depending on the scale of the Dock, which (for a full Dock) varies depending on the number of items in it.

I note incidentally that any one of the following changes would solve my particular problem, but I believe that what I have described above is most relevant thing to report because it is the most bug-like rather than additional-feature-like.

1. Fix this bug: adjust rendering to match the actual window size.
2. Add a launcher option to maximize the window on launch, rather than taking a specific numeric size.
3. Have the game's fullscreen option use modern macOS fullscreen mode (as can be done using the green window button but has to be clicked every time you start the game) rather than the old style one which also interferes with switching to other applications.