I've been able to launch Minecraft in Boarderless window mode using the following JVM Arguments command:
 -Dorg.lwjgl.opengl.Window.undecorated=true

This is a somewhat well known trick that I've been using for many years with absolutely no problems. This evening my Minecraft launcher updated to the latest version, and now whenever I launch an instillation the game shows up as a small window. I've tried editing the screen resolution and no matter what I set it too the window size remains unchanged.

I'm not sure if this could be a change in the new launcher effecting resolution that could be causing this? This has never happened before and I'm not sure where to go for help about this. If there is a change to the launcher that is causing this I was hoping someone could look into it. Thank you so much in advance!