I'm running Windows 10, the resolution is 1386x768. Does anybody know?

Go to C:\Users\[YOUR USER NAME]\Documents\My Games\MajestyHD.

Open MajXPrefs with Notepad, and change this:

<Windowed>1</Windowed>

to this:

<Windowed>0</Windowed>

Do note that that may cause issues on some systems, mostly manifesting in the game running very slow.

Did you try change compatibility to Win 7 or older?

Is there any possibility to run the game in full window mode and full speed? When I run it in full mode it's unplayable because it's so slow and when I run it in window mode it's very exhausting for my eyes since everything is so little...

Again, full screen apparently causes issues on some systems.

As for the resolution, yes, everything appearing "little" is the game's display not being scaled from a small resolution (I wonder how few people actually understand this from various forum replies) when it's windowed. The only thing you can do in windowed mode is change the resolution to increase or decrease the view range, but not the scaling.

<DataGroups>
<PixWidth>1920</PixWidth>
<PixHeight>1080</PixHeight>
<PixDepth>32</PixDepth>
<Windowed>0</Windowed>
<DebugFlags>0</DebugFlags>
<VSync>1</VSync>
<BlitMode>1</BlitMode>
<IntroVideo>0</IntroVideo>
</DataGroups>

Working setup.