Who needs a debug probe, if you have printf()? If doing serious development, you most likely want a hardware debug probe. Erich Styger dives into the subject:

We at the HSLU IET use different hardware, boards and kits, and for many of the classroom equipment it is very useful to have the debug probe embedded on the target board: less cables, easier to use. For this we have developed a new Open Source Hardware (OSHW) debug probe in KiCad which can used in different ways: as external debug probe, integrated and soldered on top of the target board, or fully integrated and embedded into a custom design.

The goal was to make it open, smaller and versatile:

• Open Source Hardware design with KiCad
• Binary firmware compatibility with MCU-Link (NXP LinkServer, CMSIS-DAP, ARM DAPLink)
• Dual-Layer design for lower costs
• USB-C connector instead of Micro-USB
• USB-C connector usable to debug the LPC55S69
• 3D printable enclosure
• BOM with assembly costs: ~$12/piece for 100 units (e.g. PCBWay), and more

Read more in the post here. All the design files are available on GitHub.