Boost it and abandon it. This will give private space goers a place to go in space, like diving a wreck in the ocean or crash it on the moon .

Might be time to invite participation by China. They ain't broke. Regardless, de-orbiting ANYTHING that we paid good treasure to put on orbit is insanity. Of course, that's the modern America brand now. Used to be hard value, but now it's cost-plus insanity for the American standard.

Letting that much material de-orbit is a total waste. Break it up, re-purpose it or sell it to someone who will use it. Especially considering the cost of getting it into orbit.

Drop it on the Moon so it can be recycled and used for future constructions.

Attach a storage facility capable of holding enough food to support a maximum sized crew for however long it would take for the after effects of extinction event asteroid strike on the earth. Fill the storage facility and Park the combined craft in high orbit for obvious reasons. In the event of a significant sized asteroid being detected that is due to hit the earth, quickly get a young, fertile, mixed crew on board so that they can start the whole sorry mess all over again when it is safe to do so.
I imagine that crew selection would keep a whole army of politicians and diplomats occupied for as long as it takes for a suitable asteroid to happen our way. (One hopes they would have the common sense not to choose anyone called Adam or Eve considering the track record of the first two.)
On the other hand, we can hope that no such fate awaits us and just do whatever is the best from a cost point of view. Showing responsibility in that direction would put the space programme in good stead when it comes to justifying the cost of future publically funded science.

Ultimately, as a species, our reason for living, working, and establishing property rights in space is survival.

Why not use parts of it to construct a transplanetary ship for travel to Mars. Alternatively could be used as an outpost station at Lagrange Point 2 onthe far side of the moon, though would need a nuclear power plant akin to Curiosity to maintain orbit with ion engines. Perhaps make it into the basis of an orbiting space ship year as seems the Russians want to build. Could even be a anchor point for a space elevator on the Moon?
Just ideas. Would be a shame to waste.

Uporbit that baby when it's game over time. We can use SOMETHING from it. Private space is the only viable future. The SLS (Stupidest Launch System) is just another job destroying scam for broken people running for office.

NASA should sell it to the highest bidder. Some commercial entity could make use of it and NASA could use the money to do something useful.

sell it to the highest international bidder, or like everyone says---boost it to a graveyard orbit where it can survive until someone needs metal in outer-space.
before they practice mining on asteroids far away, they can practice salvaging and repurposing materials from the iss for delivery to orbital satellites. at the very least they should be able to scavenge the solar array with almost no re-processing.