Cannot print to serial1 on ESP32-S2

[calcut]

Hardware:

Board: Adafruit ESP32-S2 Metro
Core Installation version: 2.0.0
IDE name: Arduino IDE
Flash Frequency: 80Mhz
PSRAM enabled: yes
Upload Speed: 921600
Computer OS: MacOS

Description:

I'd like to be able to read debug/print messages from a hardware serial port (not USB).
I have connected a serial cable to the 'debug' serial port on the board. (RXD0 and TXD0 pins on the module)
https://www.adafruit.com/product/954

I can see that the connections are OK because messages are printed on every reset, but I haven't been able to print to it in the code. Am I missing something obvious?
This may be a similar issue to #5463

Sketch:

void setup() {
  Serial.begin(9600);
  Serial1.begin(9600);
}

void loop() {
  Serial.println("Serial 00");
  Serial1.println("Serial 01");
  delay(1000);
}

Debug Messages:

On serial port /dev/cu.usbmodem01
As expected I get:

12:18:51.523 -> Serial 00
...etc.

On serial port /dev/cu.SLAB_USBtoUART
I see lots of boot/debug messages, but no print messages

ESP-ROM:esp32s2-rc4-20191025
Build:Oct 25 2019
rst:0x1 (POWERON),boot:0x9 (SPI_FAST_FLASH_BOOT)
SPIWP:0xee
mode:DIO, clock div:1
load:0x3ffe6100,len:0x8
load:0x3ffe6108,len:0x1af8
load:0x4004c000,len:0x2170
load:0x40050000,len:0x1c08
entry 0x4004c4cc
I (46) boot: ESP-IDF v4.3-dev-1197-g8bc19ba89 2nd stage bootloader
I (46) boot: compile time 08:34:03
I (46) boot: chip revision: 0
I (50) qio_mode: Enabling default flash chip QIO
I (55) boot.esp32s2: SPI Speed      : 80MHz
I (59) boot.esp32s2: SPI Mode       : QIO
I (64) boot.esp32s2: SPI Flash Size : 4MB
I (69) boot: Enabling RNG early entropy source...
I (74) boot: Partition Table:
I (78) boot: ## Label            Usage          Type ST Offset   Length
I (85) boot:  0 nvs              WiFi data        01 02 00009000 00005000
I (93) boot:  1 otadata          OTA data         01 00 0000e000 00002000
I (100) boot:  2 ota_0            OTA app          00 10 00010000 00160000
I (108) boot:  3 ota_1            OTA app          00 11 00170000 00160000
I (115) boot:  4 uf2              factory app      00 00 002d0000 00040000
I (123) boot:  5 ffat             Unknown data     01 81 00310000 000f0000
I (130) boot: End of partition table
I (635) esp_image: segment 0: paddr=0x00010020 vaddr=0x3f000020 size=0x0b830 ( 47152) map
I (644) esp_image: segment 1: paddr=0x0001b858 vaddr=0x3ffbfbe0 size=0x01f24 (  7972) load
I (646) esp_image: segment 2: paddr=0x0001d784 vaddr=0x40024000 size=0x02894 ( 10388) load
I (655) esp_image: segment 3: paddr=0x00020020 vaddr=0x40080020 size=0x224b8 (140472) map
I (687) esp_image: segment 4: paddr=0x000424e0 vaddr=0x40026894 size=0x09348 ( 37704) load
I (696) esp_image: segment 5: paddr=0x0004b830 vaddr=0x50000000 size=0x00010 (    16) load
I (703) boot: Loaded app from partition at offset 0x10000
I (703) boot: Disabling RNG early entropy source...
[     0][D][esp32-hal-tinyusb.c:580] tinyusb_enable_interface(): Interface CDC enabled
[  1240][D][esp32-hal-tinyusb.c:441] tinyusb_load_enabled_interfaces(): Load Done: if_num: 2, descr_len: 75, if_mask: 0x10
[  1457][D][esp32-hal-psram.c:84] psramInit(): PSRAM enabled

[me-no-dev]

Use Serial0 when USB is Serial