even if some public land was fully blocked in by private land, the public still has every right to access that land. If that means moving through private land to get to it, so be it. If the owner dont like it, they can sell and buy some other land that is less public-adjacent.
If there's too much paperwork involved in eminent-domaining every one of these, you could have a system where members of the public can request corner access, and some agency can invoke eminent domain in priority order based on the number of requests for each corner.
Private owners are generally expected to understand and establish easements.
I'm generally in favor of something like a right to roam, though I expect (many) people would ignore the part where they should be respectful of the land they are crossing.
Shouldn't anyone buying a landlocked parcel get an easement?