Take your laptop back to the Apple Store or AASP so they can examine the laptop. You have a 90 day part warranty on the repair (sometimes you may have a 90 day warranty on the whole laptop if the laptop was repaired by an Apple mail-in repair depot).
A wireless keyboard may not work to activate the Apple Diagnostics because the keyboard may not become active early enough to register the special boot keys.
Try an SMC Reset which should power off the laptop. Then try to power it on again to see if it boots. Try accessing the Apple Diagnostics again after the SMC Reset. I think your laptop is powered on which is why it is hot and why it wasn't responding to the Apple Diagnostics when using the built-in keyboard.
You don't mention which exact model you have. Some of the USB-C models have known issues with the backlight on the Display. You can try pressing the Caps Lock key on the keyboard to see if it lights up which indicates the laptop is powered on and booted to the login screen. You can also connect an external display to see if any video is on the external display. You may need to force the video to the external display by putting the laptop into Clamshell Mode by connecting a USB keyboard & mouse and closing the lid of the laptop.
