So we have our own bootloader project, was trying to get this to work in Segger Studio v6.34 Mac OS Apple Silicon and it would always fail to boot the DfuTarg, the BT would always fail advertising with error code 7 or 9. So the target would never go into DFU mode and beacon on the nRF52833DK board.
So same exact code, just downloaded an ancient Segger Studio 5.10b, and everything works. BT beacons, target goes into DFU mode and advertises DfuTarg.
Pretty sure you can try any of your DFU bootloader examples and none of them will work.