Part of the issue was definitely the over-zealous palm filtering- however I'm seeing something strange.

The finger_cnt is only 2 when you have 3 fingers down, while touch_cnt is correct.  It doesn't seem that we modify finger_cnt in the gesture library, and I haven't been able to reproduce the discrepancy on my end.  I'll dig in further after new years.

To chime in on this bug using the Apple magic trackpad 2 and dev M72:
Click and mark text does not work as intended with the trackpack.
Right now the way it is setup is:

3 finger click registers a right click.
3 fingers click and drag you can mark text.

It should be:

1 finger click and drag to mark text
2 fingers tap or click for right click. Right now 2 fingers tap does right click but two fingers click does not.

Thanks,

I did some tuning to improve click detection in this change:
http://crrev.com/c/1361880

It landed in 73 and I think it should address the issues you're seeing.

Thanks!
I see it addresses the click and drag but what about two fingers click (not two fingers tap)? It should register as a right click. Right now it does not register anything.
Any change to include these changes in M72?

It also improves two and three finger click.  The problem before was that the high pressure touches used for clicks looked like palms to the gesture library and were ignored.  I changed the palm detection thresholds and now the gesture library will classify those touches correctly.  That was the root cause for all of the errors you were seeing.

Requesting merge approval for http://crrev.com/c/1361880 into 72.  This is a configuration change applied only to the magic trackpad 2.

This bug requires manual review: M72 has already been promoted to the beta branch, so this requires manual review
Please contact the milestone owner if you have questions.
Owners: govind@(Android), kariahda@(iOS), djmm@(ChromeOS), abdulsyed@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot