Can't edit lock screen -- iOS 18.3.1 on iPhone 16 Pro Max

I have tried dozens of times to edit my lock screen and nothing works.

To edit the lock screen on iOS 18, this Apple support page Create a custom iPhone Lock Screen - Apple Support (and many other sites) say:

1. Press the side button on your iPhone twice to go to the Lock Screen.

2. Touch and hold the Lock Screen until the Customize and  buttons appear at the bottom of the screen.

3. If they don’t appear, touch and hold the Lock Screen again, then enter your passcode.

4. Tap  to create a new Lock Screen, or to make changes to a Lock Screen, swipe to the screen you want to change, tap Customize, then tap Lock Screen.

But NONE of this works for me. And I can't edit the lock screen at all.

1. Pressing the side button twice brings up the wallet, not the lock screen. But we'll let that go, because ONE press does bring up the lock screen.
2. Touching and holding the lock screen does not bring up CUSTOMIZE and + buttons. It does nothing at all.
3. If I try touching and holding the lock screen again as step 3 suggests, I will sometimes (it's unpredictable) get a message saying "use passcode to edit." But when I enter my passcode, instead of getting to any editing function, I simply get to my home screen. Other times, touching and holding the lock screen again simply does nothing.
4. I never get to step 4, the editing step, no matter what I try.

So how do I edit my lock screen, please?