We recently acquired a Dell 5290 2-in-1 and had some issues PXE booting the device using the Dell USB C dock. Altering the following BIOS settings enabled the PXE boot option
- Boot device and enter BIOS by pressing F2 at startup
- Navigate to POST Behaviour -> FastBoot and select Thorough
- Navigate to System Configuration -> USB/Thunderbolt Configurations
- Enable Thunderbolt Boot Support
- Navigate to General -> Advanced Boot Options
- Enable UEFI Network Stack
- Apply the settings and reboot the laptop
- Press F12 to enter boot options and PXE Boot should now be available