Hello,
Do you have J45 populated?
Furthermore, do you see voltage on TP30?
Since your D14 is on, SBC must generated 3.3V output.
petervlna_0-1719487840655.png
Check also J7:
petervlna_1-1719488112780.png
the K20 is powered by USB by default. you can check the TP60
petervlna_2-1719489130119.png
petervlna_3-1719489159278.png
regarding the bootloader FW:
https://mcuoneclipse.com/2016/06/26/how-to-recover-the-opensda-v2-x-bootloader/
best regards,
Peter