Stapling NM cable to panel backboard on the side of the service panel. Any NEC 2017/2020 concerns?
NM cable requires protection normally below 8’ some jurisdictions allow 7’ it is not specifically listed in code.
Since your feeder also requires protection I would suggest boxing it in code allows 1/2” Sheetrock or plywood to be used for protection.
if the flexible metal above is metal clad it would be ok if armor clad or flexible metal conduit it would also need protection. When I run into this I will attach 2x4’s then screw a piece of plywood to the 2x4 , so it can be removed.
I like plywood in this case an upside L would provide all the protection required. A short piece of 2x4 on the right and a longer one on the left then there would be no problems as the wiring would be protected.