When you start a new design, it will use the layer settings from the previous design, unless you select the Load default layer settings on new or restart option in Edit → Settings → File, in which case all the layers will have their default values.
Have you turned that option on?
In order to set the default values for all the layers that will appear in new projects, the suggestion was:
With that turned on, the Make Default button along the bottom of the full Cut Settings Editor window becomes significant, as it makes the current layer settings the default for that layer whenever you start a new project.
Have you set up the defaults for all the layers you want to load in new projects?
If so, do those default layer settings appear when you start a new project?
If you’ve turned the first option on and set the default layer values, yet those values do not appear when you start a new project, screenshots of the relevant settings will help track down what’s going on.
When you start a new design, it will use the layer settings from the previous design, unless you select the Load default layer settings on new or restart option in Edit → Settings → File, in which case all the layers will have their default values.
Double-click the layer to open the ‘Cut Settings Editor’. Once you have the defaults set the way you’d like, select ‘Make Default’ for a single layer or ‘Make Default for All’ if you want all layers to Open New with these settings.
Did you restart LightBurn after turning on the ‘Load default layer settings on new or restart’ button? I don’t remember if that is required, but wouldn’t hurt. Then do this test again, open the Blue Layer and change to Line and set the rest of the defaults for Blue, then hit Make Default.
Also, note that layers only exist where a shape has been assigned to that layer. You will not see all 29 layers when you open a new file.
As an aside, I don’t mean to distract from the main Topic but I’m noticing that your device may be configured as GRBL-M3. This is almost certainly not what you want. You probably want plain GRBL. I’d suggest editing your device and changing the type to GRBL.