How to set PWM frequency with high granuality
The short answer is, it's not trivial with a clock of 80 MHz unless you pull off some dithering techniques (see below).

$$\mathcal{f_{clk}}=PWM_{frequqncy}\times2^{steps} $$

In your case, steps required is 10 bits...therefore you need at least a main clock of 100MHz.

The document I linked in my comment, shows some complex ways to achieve this with lower clock rates by dithering and combining more timers(it is quite complex). Here is the document by STM itself.

Obviously, Another solution would be using another MCU from the same family with higher clock speeds if your application/budget allows it.