Yep.

You'll find square hole covers all over, they're not rare at all. The strength of the lid and its ability to be supported is not at all an issue on a single human sized hole - it's a thick, relatively cheap slab of metal over a small opening. They're the strongest surface of most roads, by a HUGE margin.

This piqued my interest, and it seems you're completely correct, but also the metal covers seem much more complex than what I was imagining.

https://www.randb-uk.com/product-category/ductile-iron-manho...