I am looking mostly at your parameter set.
I see $1tr=1.25mm, so your “g1 f400 x50” should be causing the X motor to make 50/1.25 revolutions.
A “g0 X50” command should move at 800mm/min, twice as fast.
The parameter set has $_pm = 2 for all 4 motors, which is very typical.
It says when you command any motion, all motors energize to hold their position if they are not generating motion. The buzzing you are hearing is the hold current being pulsed to the motor windings. The fact that you can’t turn them by hand while energized says that at least some of the windings are wired correctly and active, I believe.
$mt=2.0, so the motor leds should stay on for 2 seconds, then you should be able to manually turn the motors.
Setting $4pm=0 should turn off the led for motor 4, which you don’t have connected
The jerk parameters are on the low side but I don’t think they should cause no motion to happen. More typical values would be $xjm=5000 and $xjh=10000, same for Y. Optimal values really depend on your final machine configuration. These parameters are for a screw machine at 1.25mm/rev on X and Y.
I agree with Zootalaws, turning the power adjustments all the way up on M1-M3 would not damage anything (be careful, the pot can be damaged with too much screwdriver torque). Running full load current running a real milling job generates a lot of heat so fans blowing on tinyG are desirable. Unloaded motors require very little current to move.
Be sure to monitor your 24V supply while the motors are active for the 2 sec hold interval. It is possible that the power supply current limiter is kicking in (typically an adjustment on the power supply). If you need more time to measure, set $mt=5.0 and restart tinyG.
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