Steel seems overkill here, I’d honestly just replace that with an NTR-A grade pressure-treated wooden post. Make sure to put the factory-cut end into the ground or treat it with some tar-like wood preservative. Don’t use anything water-based as it won’t absorb into the already wet lumber.

On the top I’d just use angle brackets since those aren’t bearing any load - they’re just keeping it in place. On the bottom I’d bury a few concrete patio slabs into the ground and maybe use some kind of steel post feet to anchor it down.