Blockland does register your maximum resolution:
OpenGLDevice::setScreenMode 1400 1050 32 60 1
safeModeOn = 1
fixedFrame size = 3
caption size = 23
maxWindowWidth = 1920
maxWindowHeight = 1080
Setting screen mode to 1400x1050x32@60hz (fs)...
I also only get a max resolution of 1680x1050 if I am in normal window mode.
But once borderless or fullscreen is enabled, it gives me up to 1920x1080.
I may know a better temporary solution.
You can try setting the pref directly in the files.
Open Blockland\config\client\prefs.cs
Scroll all the way down, find the correct pref and set it like this:
$pref::Video::resolution = "1920 1080 32 60";
Can you test if it sticks after reopening the game?