I have a retaining wall made of solid stacking concrete block, not hollow. It abuts a patio of pavers. The retaining wall is a reverse wall against our house, and on another side, a drop off. I want to put a railing up and need it secure, I can tie into the corner of the house on one end, but away from that, my posts need securing.
As I see it, the choices are to pull out pavers and go down with a footing of some sort, or set it on the surface with triangulated supports on the back side, which would be ugly. The tie into the house will stabilize one end. It makes a 90 degree turn about 10 feet from that, which will help too. But the center really needs to be stable, not a wobbler.
Those who can make you believe in absurdities can make you commit atrocities- Voltaire