How to check that the Debug UART are still functional?

I made a mistake connecting the cables of the USB to TTL adapter on the Banana Pi M5. I confused the (Debug UART) GND and TxD connectors on the Banana Pi. I can type characters on the keyboard and see what the console displays. Nevertheless, I wonder if this could have damaged something on the Banana Pi. I only connected GND, RxD and RxT. I don’t know anything about serial communication but I’m trying to install OpenBSD. U-boot starts but the OpenBSD installer doesn’t display some characters like those issued by the program or the characters (strings of characters) entered by the user. Can we know if the Debug UART interface is not damaged?

...
<debug_uart>
U-Boot 2023.04-rc4-00053-g8be7b4629e (Mar 26 2023 - 13:30:03 +0200)bpi-m5

Model: Banana Pi BPI-M5
SoC:   Amlogic Meson SM1 (S905X3) Revision 2b:c (10:2)
DRAM:  1 GiB (effective 3.8 GiB)
Core:  394 devices, 28 uclasses, devicetree: separate
MMC:   sd@ffe05000: 0, mmc@ffe07000: 1
Loading Environment from nowhere... OK
In:    serial
Out:   serial
Err:   serial
Net:   eth0: ethernet@ff3f0000
Hit any key to stop autoboot:  0 
switch to partitions #0, OK
mmc0 is current device
Scanning mmc 0:1...
49690 bytes read in 4 ms (11.8 MiB/s)
Working FDT set to 8008000
No EFI system partition
No EFI system partition
Failed to persist EFI variables
BootOrder not defined
EFI boot manager: Cannot load any image
Found EFI removable media binary efi/boot/bootaa64.efi
208243 bytes read in 12 ms (16.5 MiB/s)
Working FDT set to 8008000
Booting /efi\boot\bootaa64.efi
disks: sd0* sd1
>> OpenBSD/arm64 BOOTAA64 1.12
boot>
...
"leds" at mainbus0 not configured
"regulator-emmc_1v8" at mainbus0 not configured
"regulator-dc_in" at mainbus0 not configured
"regulator-vddio_c" at mainbus0 not configured
"regulator-tflash_vdd" at mainbus0 not configured
"regulator-vddao_1v8" at mainbus0 not configured
"regulator-vddao_3v3" at mainbus0 not configured
"regulator-vddcpu" at mainbus0 not configured
"regulator-vl_pwr_en" at mainbus0 not configured
"sound" at mainbus0 not configured
simplefb0 at mainbus0: 720x576, 32bpp
wsdisplay0 at simplefb0 mux 1
wsdisplay0: screen 0 added (std, vt100 emulation)
scsibus0 at sdmmc1: 2 targets, initiator 0
sd0 at scsibus0 targ 1 lun 0: <Samsung, AJTD4R, 0000> removable
sd0: 14910MB, 512 bytes/sector, 30535680 sectors
scsibus1 at sdmmc0: 2 targets, initiator 0
sd1 at scsibus1 targ 1 lun 0: <SD/MMC, SC32G, 0080> removable
sd1: 30436MB, 512 bytes/sector, 62333952 sectors
uhub1 at uhub0 port 1 configuration 1 interface 0 "VIA Labs, Inc. USB2.0 Hub" rev 2.10/90.23 addr 2
uhub2 at uhub0 port 3 configuration 1 interface 0 "VIA Labs, Inc. USB3.0 Hub" rev 3.10/90.23 addr 3
softraid0 at root
scsibus2 at softraid0: 256 targets
root on rd0a swap on rd0b dump on rd0b
WARNING: CHECK AND RESET THE DATE!
cpu0: regulator not implemented
erase ^?, werase ^W, kill ^U, intr ^C, status ^T
���������������
Welcome to the OpenBSD/arm64 7.2 installation program.
�������(I)nstall, (U)pgrade, (A)utoinstall or (S)hell? �����������������s��������������������������������������

Addendum: Everything the user enters in the serial console (after the OpenBSD installer started) appears as a sequence of ���������.

I did the Armbian installation to see if there was a difference. No problem. However, I don’t know if I can properly shut down the Banana Pi M5 using serial communication (c.f. Error: Power switching is denied by A55!!).

...
bl30 enter suspend!
Little core clk suspend rate 1000000000
Error: Wait for CPU3 Power off state timeout
Error: Wait for CPU2 Power off state timeout
Error: Wait for CPU1 Power off state timeout
Error: Wait for CPU0 Power off state timeout
Error: Power switching is denied by A55!!
Error: wait power state change failed
store restore gp0 pll
store restore gp1 pll
suspend_counter: 1
Enter ddr suspend
ddr suspend time: 17us
alarm=0S
process command 00000001
cec ver:2018/07/03
CEC cfg:0x0000
WAKEUP GPIO cfg:0x00000000
set sd power off
set 5v power off
08915d0000000000set_remote_mode 0x00000000WAKEUP GPIO FAIL - invalid key 
fffffe71
kern log_addr:0x00
cec T: 00
err: tx not finish flag
cec reset
Set cec pinmux:0x11
Set cec log_addr:0x10,ADDR0:10

It’s what the console displays that worries me about the state of the Debug UART.

08915d0000000000set_remote_mode 0x00000000WAKEUP GPIO FAIL - invalid key 
fffffe71