You are confusing "proportional representation" (an outcome which many systems approach) with Party List Proportional (an election method which is designed to achieve proportional representation.)
There is no Constitutional barrier to many PR systems (e.g., STV in multimember districts) in the US, though there are some structural limits to the degree of proportionality that could be achieved (you'd still have to apportion by population and have each state as a separate pool.)
There are some federal statutory limits mandating single-member districts, but those are much easier to reform than Constitutional barriers.
> Every time I see a thread here I really do look forward to reading thoughts that are actually about gerrymandering and solving gerrymandering
Distortions of the kind labelled gerrymandering are fundamental to the exclusive use of independent single member districts (and exacerbated if you use plurality or majority-runoff elections in those districts.)
This is an inescapable fact. You can't complain that you want to hear solutions to gerrymandering and simultaneously exclude all the things that actually address gerrymandering from the acceptable solution space. Well, you can, but you are making irreconcilably conflicting demands when you do so.