I speak a little Spanish, but no Portuguese, and my time in Brazil right near the border with two Spanish speaking countries was a challenge, because most folks there didn’t speak Spanish despite the location.
Some folks do of course, but most people I encountered didn’t have any Spanish
I have zero idea how representative that is of other borders
Yep, Iguazú. I likely felt it because my Spanish is not great, so even though I could make myself understood by Argentinians, the poor Brasilians stood no chance as I murdered Spanish in an attempt to communicate :)