Help for powering a LattePanda 3 Delta cyberdeck

Hello. To begin with, I am not (too) technically inclined and know bare minimum about power (watts, volts, amps, etc). I am planning on building a cyberdeck using a LattePanda 3 Delta.

I would like to have a mechanical switch/knob that will switch the power from 'Wall Power' to 'Battery Power', without the LattePanda cutting out as the Wall Power to Battery Power switch is triggered (I understand there might be a split second or more when the physical switch is triggered when the Wall Power is turned off and before the Battery Power kicks in). I think for that, I will need to install a capacitor somewhere so as the power is switched from Wall to Battery (or back) the capacitor will feed enough power so the LattePanda doesn't shut off as the switch is 'switching' power sources. Do I have that part right?

I plan to power the 9 inch touch screen monitor via the USB port on the LattePanda. A case fan (small), USB mechanical keyboard (no RGB or any bells and whistles), usb mouse (non RGB) and small track pad will all also draw their power from the LattePanda. So, the Wall Power and Battery Power just need to power the LattePanda directly, and nothing else directly. I think the monitor will draw around 1A. The balance of the USB connected devices should be around 0.5A in total, but I'll round up and assume 1A for those too. The LattePanda documentation states that it "Accepts Power Delivery compliant devices at 15V 3A or 12V 3A " via USB-C or can take 12-volt input from JST PH2.0-4Pin connector on the board. Based on this - am I going to be able to even power all the USB devices connected to the LattePanda as planned?

Assuming I can (or if there is a better solution to what I have proposed above), how do I set it up properly so I can have a physical switch/knob to instantly change from Wall Power to Battery Power (or vice versa), 'on the fly'. I can put the batteries inside the Cyberdeck - there will be a lot room for this. I am just not sure the best way to manage this.

Thanks much for any help. Again, please consider me to be less intelligent than a 10 year old about electrical systems, circuits, switches, etc. if you are kind enough to offer any advice here.

Cheers!