I did not get the same number as in the following statement:
Since 1984, the Stockholm Stock Exchange (OMXS30) has risen by over 3,000 percent. This means that the stock market has risen by an average of 7 percent per year.
I get instead (1.07)^(2023-1984)=14, that would mean 14 times the money in return, so the rise would be 13 units i.e. 1300%. If I invested 1 unit in 1984 at 7 % compounded interest rate, at the end of year 2022 it would be worth 1.07 × 1.07 × 1.07 × 1.07 × ... = 14. It does not look like +3000% so there is some mistake somewhere but where?
I agree with you, but such statements often have poor arithmetic. $\sqrt [39]{30} \approx 1.09$, so the return is about $9\%$ per year. Certainly I would not count on "risen by $3000\%$" to mean $1$ turns into $31$ instead of $30$ and it won't change the result much anyway.