What about variable frequency switching power supplies?
To regulate to a certain voltage with DC-DC switching, you generally vary the duty cycle of the driver waveform. There’s several techniques to do that, including these two well-known methods:

fixed frequency, variable duty cycle (PWM)
fixed on-time, variable off-time (sometimes called COT, constant on-time)

In reality regulators may use more than one method depending on the load condition. And between each type, there are trade-offs for ripple vs. efficiency vs. transient response.
There’s also finer details about the type of control loop (e.g., current mode, voltage mode, etc.) that influences the regulator choice.
Lately, I’m tending to use COT for high-current supplies with fast transients, since holding the voltage above a minimum is more important than accuracy (logic core supply.)
For more noise-sensitive supplies fixed frequency PWM is preferred which, while it responds more slowly to transients, will have less (or more predictable) ripple.
MORE: (shout out to John D for the comment) There’s a newer, more-efficient topology that in fact uses frequency: LLC resonance. In broad strokes, this type adds a tuned L-C circuit inline with the switch. The power delivered to the load is adjusted by varying the PWM frequency to above or below the L-C resonance point to create a regulator loop.
LLC resonance supplies are  more complex than PWM but have the advantage of lower switching losses. More here: https://www.electronicdesign.com/power-management/article/21805811/llc-resonant-converters-raise-the-powerefficiency-bar