If you’re an anarchist, then it would be illogical for you to argue that the US government should sell off federal land in order to divest itself of property. Instead, the logical argument should be that the federal government should vacate the land it has taken possession of and not interfere with its original owners’ resettlement.
For, if you argue that the government should sell the land it holds, then you are implicitly admitting that the government is a) a legitimate entity and that b) it possesses property rights. If the government were an illegitimate entity, then whatever ownership claims it would make would subsequently be illegitimate as well. Thus, it would have to forfeit all claims to the proceeds of the sales, since those claims are derivative from the initial illegitimate ownership claim.