separate window

This seems to work,

For the custom code snippet do

either just org.lwjgl.util.tinyfd.TinyFileDialogs.tinyfd_messageBox("Test", "Haiii", "ok", "error", true);

or,

Thread thread = new Thread(() -> {
	org.lwjgl.util.tinyfd.TinyFileDialogs.tinyfd_messageBox("Test", "Haiii", "ok", "error", true);
});
thread.start();

difference is that for the second one the client rendering won't freeze

# Make sure that the procedure you call it in is run on the client, aka it doesn't say this,

if it says that you have to set a global variable and then do the org.lwjgl.util.tinyfd.TinyFileDialogs.tinyfd_messageBox("Test", "Haiii", "ok", "error", true);

"On player tick update"