New to Trackpad. Drag Lock Not Working as Expected?

Very odd. Sorry for the basic question, but first let's confirm you are tapping and not clicking on the trackpad.

• the file will open in its associated app, or

So a normal double-tap, as if you didn't hold down the second tap. With Use Trackpad for Dragging turned OFF, a double tap with the second tap held has no effect, the item doesn't open.

• when I begin to drag, it will select all other files along my drag path (as if I were shift-clicking to select multiple files), or

So as if you click on the desktop and not on an item, and you're seeing the drag-to-select box.

• it will just behave like a regular drag/drop (when I release my finger it drops the file in the location I happen to be hovering over) instead of locking in place so I can readjust my finger.

So as if you are clicking-and-dragging or double-tapping and dragging, but without drag lock.

Yeah, none of those are normal behaviors.

My settings are close to yours (the differences should not matter for this, e.g., I use Force Click and I have two-finger zoom enabled).

I doubt it's the trackpad. I'm using a Magic Trackpad with USB-C (on an M4 Pro MBP in clamshell mode):

But I connected an older Magic Trackpad 2 (with the Lightning Connector) that was sitting in a drawer and drag lock works as expected, same as my current trackpad.

The next thing I'd try is to see if the problem is present when you boot in safe mode, which disables 3rd party extensions and performs some system cleanup.

Start up your Mac in safe mode - Apple Support

If that doesn't help, one other common troubleshooting step is to create a new user account and see if behavior is normal there.

Add a user or group on Mac - Apple Support

If those don't work, perhaps contacting Apple is your next step. Either a Genius Bar appointment, or contact Apple's dedicated Accessibility support team (since that's where the drag lock setting lives).

Accessibility Support - Official Apple Support

Your settings look correct. What you need to do is double-tap the item and keep your finger on the trackpad after the second tap, then start dragging. After you start the drag, then the item is 'drag locked'. At that point, you can lift your finger from the trackpad and the item will remain draggable. You will see the item's original location on the desktop and a copy of it that moves around as you move your finger. You then move it where you want and tap once to drop the item.

If it works in Safe Mode, that suggests a 3rd party extension is causing the issue. However, simply rebooting normally after safe mode may have fixed it (the cleanup does that for some issues) so before going further, that would be the first thing to check if you have not done so already.

Not sure if you were able to install software, but the free EtraCheck (written by a long time community member here) will list all of the extensions you have installed, along with general system information but nothing private. You can post the report using the additional text button (between the link and image insertion buttons).

The 'copy' effect is the normal even without drag lock. This is a regular click-and-drag without drag lock enabled.

If you double tap, hold the second tap and start to drag, does the item move?

Possible that you're not double-tapping fast enough. You can try tapping faster, or slow down the speed needed in System Settings > Accessibility > Pointer Control.