How though? I mean I agree being royal adjacent is what Harry wants, but there's the Windsor family and then there's the institution. The institution is paramount, along with the security of the state and William being able to take the throne with some breathing space, free of all the shite his parents created. Charles giving Harry an audience on a purely personal basis to make their personal peace before Charles passes away, imo, protects William and Catherine against accusations that they prevented him from seeing Harry, and that being Harry's gripe for the next 40 years, hugging Charles' grave and complaining of an injustice.
For the avoidance of doubt, I do not think that Charles should go any further than that - no Invictus appearance or anything else that makes Harry look like a quasi working royal. No self flagellation about the past or promises for the future, especially no promises on behalf of William. No public meetings, and make the fucker sign an NDA. Any leaks or interviews giving details and it ends. The public shouldn't even know when it's happening. Just a case of come and see me, show me photos of the children, have a pleasant chat and off you go, maybe see you in a couple of months for the same.
It's obviously not ideal, and after everything Harry has said and done, even that little amount of time and access feels like far too much grace. But what's the alternative? If Harry is offered this limited access, but access nevertheless to spend time with his father, and he turns it down or demands more, or starts on about security and inheritances, or moans to the press, then the palace will know he's not really interested in re-kindling an emotional Charles, and they can can it.
I freely admit I may be being hopelessly naive!