Remove the delay in macOS' touch and drag mode. It still doesn't fire events during the delay yet it removes the sticky effect.

touchAndDragDelay.c

// clang -o touchAndDragDelay touchAndDragDelay.c -framework ApplicationServices -F/System/Library/PrivateFrameworks -framework MultitouchSupport
/*
~/Library/LaunchAgents/uk.co.mishurov.touchndrag.plist
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>uk.co.mishurov.touchndrag</string>
    <key>Program</key>
    <string>/Users/path/to/touchAndDragDelay</string>
    <key>KeepAlive</key>
    <true/>
</dict>
</plist>
launchctl load uk.co.mishurov.touchndrag.plist
*/
 
#include <ApplicationServices/ApplicationServices.h>
 
 
typedef struct { float x,y; } mtPoint;
typedef struct { mtPoint pos,vel; } mtReadout;
 
typedef struct {
    int frame;
    double timestamp;
    int identifier, state, foo3, foo4;
    mtReadout normalized;
    float size;
    int zero1;
    float angle, majorAxis, minorAxis;
    mtReadout mm;
    int zero2[2];
    float unk2;
} Finger;
 
typedef void *MTDeviceRef;
typedef int (*MTContactCallbackFunction)(int, Finger*, int, double, int);
 
MTDeviceRef MTDeviceCreateDefault();
void MTRegisterContactFrameCallback(MTDeviceRef, MTContactCallbackFunction);
void MTDeviceStart(MTDeviceRef, int);
 
enum Mode {
    Normal,
    Dragged,
    Released
};
static enum Mode mode = Normal;
 
int callbackMultitouch(int device, Finger *data, int nFingers,
                    double timestamp, int frame)
{
    for (int i = 0; i < nFingers; i++) {
        Finger *f = &data[i];
        // only first contact is of interest
        // state == 4 is a contact press
        // state == 7 is a contact release (on ELAN1200)
        if (mode != Dragged || i > 0 || f->state != 7)
            return 0;
        mode = Released;
#ifdef DEBUG
        printf("Frame %7d: Angle %6.2f, ellipse %6.3f x%6.3f; "
            "position (%6.3f,%6.3f) vel (%6.3f,%6.3f) "
            "ID %d, state %d [%d %d?] size %6.3f, %6.3f?\n",
            f->frame,
            f->angle * 90 / atan2(1,0),
            f->majorAxis,
            f->minorAxis,
            f->normalized.pos.x,
            f->normalized.pos.y,
            f->normalized.vel.x,
            f->normalized.vel.y,
            f->identifier, f->state, f->foo3, f->foo4,
            f->size, f->unk2);
#endif
    }
#ifdef DEBUG
    printf("\n");
#endif
    return 0;
}
 
static CGPoint location = {0};
static CGEventSourceRef source;
 
void postMouseEvent(CGEventTapProxy proxy, CGEventType eventType) {
    CGEventRef event = CGEventCreateMouseEvent(source, eventType,
                        location, kCGMouseButtonLeft);
    CGEventTapPostEvent(proxy, event);
    CFRelease(event);
}
 
 
CGEventRef callbackQuartz(CGEventTapProxy proxy, CGEventType type,
                CGEventRef event, void *refcon)
{
    if (type == kCGEventLeftMouseDragged) {
        location = CGEventGetLocation(event);
        if (mode == Released)
            postMouseEvent(proxy, kCGEventLeftMouseUp);
        else if (mode == Normal)
            mode = Dragged;
    } else if (type == kCGEventLeftMouseUp && mode != Normal) {
        mode = Normal;
    }
    return event;
}
 
 
int main(int argc, char **argv)
{
    CFMachPortRef eventTap = NULL;
    CGEventMask eventMask = 0;
    CFRunLoopSourceRef runLoopSource = NULL;
     
    source = CGEventSourceCreate(kCGEventSourceStateHIDSystemState);
    eventMask = CGEventMaskBit(kCGEventLeftMouseDown) |
        CGEventMaskBit(kCGEventLeftMouseUp) |
        CGEventMaskBit(kCGEventRightMouseDown) |
        CGEventMaskBit(kCGEventRightMouseUp) |
        CGEventMaskBit(kCGEventLeftMouseDragged) |
        CGEventMaskBit(kCGEventRightMouseDragged) |
        CGEventMaskBit(kCGEventScrollWheel);
    eventTap = CGEventTapCreate(kCGSessionEventTap, kCGHeadInsertEventTap,
                    0, eventMask, callbackQuartz, NULL);
    if (NULL == eventTap) {
        printf("ERROR: failed to create event tap\n");
        goto fail;
    }
 
    runLoopSource = CFMachPortCreateRunLoopSource(kCFAllocatorDefault, eventTap, 0);
    CFRunLoopAddSource(CFRunLoopGetCurrent(), runLoopSource, kCFRunLoopCommonModes);
    CGEventTapEnable(eventTap, true);
 
    MTDeviceRef dev = MTDeviceCreateDefault();
    MTRegisterContactFrameCallback(dev, callbackMultitouch);
    MTDeviceStart(dev, 0);
 
        CFRunLoopRun();
fail:
    if (NULL != eventTap) {
        CFRelease(eventTap);
        eventTap = NULL;
    }
 
    if (NULL != runLoopSource) {
        CFRelease(runLoopSource);
        runLoopSource = NULL;
    }
    return 0;
}