I can not set the public / anonymous Access to my confluence site.
You've not said why you think you can't set it (can't find the option, can't see it where it should be, large penguin sitting on your keyboard...), so here's a brief overview to cover most of the reasons you might fail:
To enable anonymous access, you need to enable it
Now two quirks:
That should cover can't find/can't see. (I can't tell you more about the penguin, I don't know if he's one of my friends)
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