We already have that. Each state gets allocated a number of representatives in proportion to its population, which, in turn, determines the number of congressional districts in that state.

I believe they meant to have only a single congressional district per state, with multiple representatives allocated to parties proportionally according to election result.

Proportional representation is the most common electoral system for national legislatures (and is also used by e.g. EU parliament).

https://en.wikipedia.org/wiki/Proportional_representation

Seven US states have "at large" congressional districts, and a few states have one at large district. This seems easier and maybe more sensible for a state's representatives in the US Congress. [0]

Apparently, there used to be more at large states, except states were using it to dilute minority votes. (The white majority was large enough to elect all-white representatives.) In 1986, this was ruled to violate the 1965 Voting Rights Act. [1]

[0] https://en.wikipedia.org/wiki/At-large

[1] https://en.wikipedia.org/wiki/Thornburg_v._Gingles

Yes, exactly.