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Valid points. The existing post has essentially disconnected at ground level to what was in the ground. I'm thinking something like the linked as solutions (either metal or concrete spur), with then i guess some postcrete around it (have never worked with concrete/postcrete etc, is this simple?)
https://www.diy.com/departments/forest-garden-concrete-repair-spur-w-75mm/5013053172780_BQ.prd
You could try those spurs you hammer into the ground and put the post into, but the problem with those is that if they hit any rock under the surface they either stop or bend/break.
If you don't want annual repairs, just dig a hole and postcrete it in. My fence took 2 weekends of work, and that's only because our house was built on an old industrial site and I had to chisel rubble out of the way.