When I was very active in autocross competition many years ago, I noted that many top competitors used left-foot braking, even with manual gearbox cars. It is also common in other areas of motorsports. I learned to do it by practicing with auto-trans vehicles first. I used it occasionally in competition with manual gearbox cars, but now I routinely left-foot brake in all non-manual vehicles. When driving my manual vehicle I automatically switch to normal right-foot braking.
With left-foot braking the probability of a UA error is greatly reduced. Modern auto vehicles and EV's stop or greatly restrict acceleration when the brake is engaged. Even in older vehicles the brakes are more powerful than the engine. Learning the technique takes commitment as one needs to develop left-leg muscle memory for the proper inputs to the brake pedal.
There are many discussions of left-foot braking in competition. Here is one in reference to street driving:
Why You Should Be Braking With Your Left Foot