I think that people can still have a shared reality as long as they understand that there is a disagreement. For example, Google could have done what many map makers do and explicitly indicate where borders are disputed.

It seems like you are getting hung up on the idea that "real" means that something can be proven using physical laws. For most people in most circumstances, that's not a particularly useful way of defining real. Usually, "real" is defined as something like "the facts on the ground that impact our lives".

Take for example, Taiwan. The facts that people mean when they talk about Taiwan's borders being real are something like: Taiwan's status is in dispute between China and most of the rest of the world. In order to maintain diplomatic relations and prevent war, most of the world has adopted a policy of officially ignoring the dispute while unofficially supporting Taiwan's independence. In terms of day to day governance, Taiwan is independent from China. For example, the reality of the Taiwanese border is that there is a dispute between China and most of the rest

I've got no problem with people informally using the word real in the way you suggest (and in fact I only reference things like electron charge as exemplars of the objective, not to suggest that we can only speak of the brutally physical as real). Nevertheless, however, asserting that a border is "real" or ought to be thought of as real is not a description of "the facts on the ground that impact our lives," it is an assertion that some particular state of affairs should be acceded to by some set of people. Characterizing it as a dispute about reality is deeply disingenuous.

> I think that people can still have a shared reality as long as they understand that there is a disagreement. For example, Google could have done what many map makers do and explicitly indicate where borders are disputed.

But that's exactly what they do already, when allowed to.

Have a look at Jammu Kashmir. If you're not located in India or Pakistan, the disputed borders are shown as dotted lines rather than the normal solid lines for national borders. If you look at the details of any location in the region (e.g. the city of Jammu), it won't show any country.

Now, if you're in India, it'll not display any disputed borders and instead show the entire area being a part of India. But showing the dotted line isn't an option, showing these borders is required by the local laws. And you wouldn't want a multinational company to try to flout the laws of the countries they're operating in, would you?

>[...] nation states have rarely agreed, as a matter of course, on where boundaries are [...]

There are far far more contemporary examples of nations agreeing on where the boundaries are than examples of them not agreeing. The status quos is generally agreement.

I'd be willing to hazard a guess that very few borders on earth between nation states have no disputed areas, but in any case, even if this were true it is a state of affairs no more than a few hundred years old and many borders were arbitrarily drawn by world powers sometimes even for sinister reasons (for a good example, read about the border between Armenia and Azerbaijan). Throughout most of history firm borders were simply impossible to define. I object strongly to raising them to the level of a "shared reality."