After filtering time & sales for only trades greater than 9,999 this is what I got:
1600:01 16,655,878
1600:02 417,618
1600:02 27,860
1600:03 13771
1600:19 686,502
1600:19 12,454
1600:28 20,022
1600:41 116,567
1600:41 52,936
1600:42 120,424
1600:42 120,424
1600:42 25,428
1601:59 49,426
1602:52 204,623
1602:55 11,545
1602:58 111,832
1603:00 56,874
1603:01 29,253
1603:07 156,215
1603:10 15,904
1603:13 11,512
1603:14 29,874
1603:15 112,592
1603:15 219,230
1603:16 383,100
1603:16 161,839
1603:17 89,160
1603:22 27,421 *
1603:22 19,665 *
1603:43 222,741
1604:54 42,352
1605:14 44,000
1605:23 14,268
1605:26 11,000
1605:28 21,861
1605:31 44,000
1605:32 46,961
1605:33 35,866
1605:36 64,669
1605:41 30,600
1610:45 137,102
1612:31 86,333
1613:19 53,922
1614:21 119,742
1614:21 369,426
1620:54 3,680,751 *
1631:46 14,510
1641:40 10,595
1752:04 10,773
Note all traded at the bid/down ticks @ $121.26 except 3.68m was $121.28, and 27,421 and 19,665 were $121.27. There also was of course a shitload of $121.26's lot sizes 9,999 shares and lower as well as many other trades at many other prices. Be curious what a market profile of after hours looks like to setup Monday's action.
As some others have mentioned, very likely Cathie Wood/Ark or some other fund was the single large seller behind it.
HTH