I am using a Unicomp Mini M 2023 Japanese keyboard. I have an oldish USB2USB converter from 2018 and it worked without any modification. But then I tried to modify my keyboard layout and all keys stopped working. I am using the converter so that the Japanese keys such as pc_katakana are reported to the non-Japanese Windows operating system (EN UK).
Here is the purchase page for the Unicomp keyboard:
https://www.pckeyboard.com/page/product/MINI_MThe modification was made using the  TMK Keymap Editor and the generated hex file from there. Flashing was done with QMK Toolbox with ATmega32U4 selected.
Subsequently I flashed usb_usb_debug.hex
usb_state: 20
usb_state: 40
usb_state: 50
usb_state: 51
BM Init
Addr:01
NC:01
HID_PROTOCOL_KEYBOARD
bNumEP:02
Cnf:01
bIfaceNum:00
bNumIface:00
Interface:00
SET_PROTOCOL: 00
SET_IDLE: 00
RPIPE: 00
RWU: 00
BM configured
host.Task: 2318
usb_state: 90
speed: full
and see that "ignored" on all keypresses is reported.
Finally, I tried to flash usb_desc_dump.hex via QMK Toolbox, but I got an Error reading line 1.
The information about the keyboard itself :
$ lsusb -d 17f6:1862 -v
Bus 001 Device 004: ID 17f6:1862 Unicomp, Inc. U AP1_4_87k_Kbrd_v7_53
Couldn't open device, some information will be missing
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            0 [unknown]
  bDeviceSubClass         0 [unknown]
  bDeviceProtocol         0 
  bMaxPacketSize0         8
  idVendor           0x17f6 Unicomp, Inc.
  idProduct          0x1862 U AP1_4_87k_Kbrd_v7_53
  bcdDevice            7.53
  iManufacturer           1 Unicomp Inc
  iProduct                2 U AP1_4_87k_Kbrd_v7_53
  iSerial                 0 
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength       0x0022
    bNumInterfaces          1
    bConfigurationValue     1
    iConfiguration          3 
    bmAttributes         0xa0
      (Bus Powered)
      Remote Wakeup
    MaxPower              100mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           1
      bInterfaceClass         3 Human Interface Device
      bInterfaceSubClass      1 Boot Interface Subclass
      bInterfaceProtocol      1 Keyboard
      iInterface              4 
        HID Device Descriptor:
          bLength                 9
          bDescriptorType        33
          bcdHID               1.11
          bCountryCode           33 US
          bNumDescriptors         1
          bDescriptorType        34 Report
          wDescriptorLength      63
          Report Descriptors: 
            ** UNAVAILABLE **
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x000c  1x 12 bytes
        bInterval               2
Oh, and one more thing: The converter used to light up, and now it does not.
Any help is appreciated.