TSMC's 5 nm production is mostly focused on Apple's A14 Bionic SoCs and apparently cannot meet the projected order volume for the M1 chips. Since Samsung is the only other foundry to have operational 5 nm nodes, the South Korean foundries could once again become an Apple supplier. Nevertheless, the low yields on Samsung's 5 nm nodes might lead to sub-par performance on some M1 chips.
https://www.notebookcheck.net/TSMC-cannot-meet-the-entire-Apple-M1-order-volume-Samsung-could-jump-to-the-rescue.503905.0.html