Well usually what we call ”FET” drivers are direct drive, as you said they just have modes = fixed duty cycles.
There are also linear constant drivers that adjust the gate-source voltage of a Nchannel MOSFET to adjust its resistance and thus the current, this is similar to 7135 chips, except a 7135 can only be dimmed with PWM.
This is mistaken though, driving a LED with PWM doesn’t mean there is no loss, it’s just that the heat is generated (mainly) in the LED instead of in the driver, there are also RMS current conduction losses (significant in multi LED lights due to the on current being very high), in the end a linear driver is more efficient than a PWM driver, although a good buck driver is obviously better.
I designed a few Anduril (e-switch) linear driver here with building instructions (I’m going to receive the new boards in a few days and test them).
Led4Power sell CC linear drivers for clicky switches.
Convoy also sells different sizes in 5 and 6A for clicky switches, they are called ”SST-40” driver.