I’d say the most impactful thing is not to learn SQL, but set theory.

Well-written SQL is about thinking in sets. I cannot tell you how many poorly written procedural stored procedures I’ve replaced with a single performant SQL query over the years.

This is because the most impressive part of the SQL ecosystem is the DBMS engine’s query plan. Though, yes, you have to know how to influence it.

I find ORMs also tend to keep devs thinking procedurally.

Yes learn SQL! But don’t just learn the syntax. Learn the underlying mathematical models and ways of thinking that SQL supports implementing.