How to upgrade a SoloKey firmware

solokey-bash.log

// See https://github.com/conorpp/solo-dicekeys/releases/tag/5.0.0
$ solo version
0.0.27
$ python3 --version
Python 3.9.0
$ solo ls
:: Solos
208B31985653: Solo 4.1.1
 ~ $ pip3 install --upgrade solo-python
Requirement already satisfied: solo-python in /usr/local/lib/python3.9/site-packages (0.0.27)
Requirement already satisfied: cryptography in /usr/local/lib/python3.9/site-packages (from solo-python) (3.4.6)
Requirement already satisfied: pyusb in /usr/local/lib/python3.9/site-packages (from solo-python) (1.1.1)
Requirement already satisfied: click>=7.0 in /usr/local/lib/python3.9/site-packages (from solo-python) (7.1.2)
Requirement already satisfied: fido2~=0.8.1 in /usr/local/lib/python3.9/site-packages (from solo-python) (0.8.1)
Requirement already satisfied: pyserial in /usr/local/lib/python3.9/site-packages (from solo-python) (3.5)
Requirement already satisfied: requests in /usr/local/lib/python3.9/site-packages (from solo-python) (2.25.1)
Requirement already satisfied: ecdsa in /usr/local/lib/python3.9/site-packages (from solo-python) (0.16.1)
Requirement already satisfied: intelhex in /usr/local/lib/python3.9/site-packages (from solo-python) (2.3.0)
Requirement already satisfied: cffi>=1.12 in /usr/local/lib/python3.9/site-packages (from cryptography->solo-python) (1.14.5)
Requirement already satisfied: pycparser in /usr/local/lib/python3.9/site-packages (from cffi>=1.12->cryptography->solo-python) (2.20)
Requirement already satisfied: six>=1.9.0 in /usr/local/lib/python3.9/site-packages (from ecdsa->solo-python) (1.15.0)
Requirement already satisfied: cryptography in /usr/local/lib/python3.9/site-packages (from solo-python) (3.4.6)
Requirement already satisfied: six>=1.9.0 in /usr/local/lib/python3.9/site-packages (from ecdsa->solo-python) (1.15.0)
Requirement already satisfied: certifi>=2017.4.17 in /usr/local/lib/python3.9/site-packages (from requests->solo-python) (2020.12.5)
Requirement already satisfied: idna<3,>=2.5 in /usr/local/lib/python3.9/site-packages (from requests->solo-python) (2.10)
Requirement already satisfied: urllib3<1.27,>=1.21.1 in /usr/local/lib/python3.9/site-packages (from requests->solo-python) (1.26.2)
Requirement already satisfied: chardet<5,>=3.0.2 in /usr/local/lib/python3.9/site-packages (from requests->solo-python) (4.0.0)
 ~ $ solo key version
4.1.1 unlocked
 ~ $ solo key
Usage: solo key [OPTIONS] COMMAND [ARGS]...

  Interact with Solo keys, see subcommands.

Options:
  --help  Show this message and exit.

Commands:
  challenge-response  Uses `hmac-secret` to implement a challenge-response...
  change-pin          Change pin of current key
  credential          Credential management, see subcommands.
  disable-updates     Permanently disable firmware updates on Solo.
  keyboard            Program the specified key sequence to Solo
  make-credential     Generate a credential.
  ping                Send ping command to key
  probe               Calculate HASH.
  reset               Reset key - wipes all credentials!!!
  rng                 Access TRNG on key, see subcommands.
  set-pin             Set pin of current key
  sign-file           Sign the specified file using the given credential-id
  update              Update Solo key to latest firmware version.
  verify              Verify key is valid Solo Secure or Solo Hacker.
  version             Version of firmware on key.
  wink                Send wink command to key (blinks LED a few times).
 ~ $ solo key verify
Please press the button on your Solo key
Register valid
Solo Hacker firmware.
 ~ $ solo ls
:: Solos
208B31985653: Solo 4.1.1
 ~ $ cd ~/Desktop/
bundle-hacker-5.0.0.hex
bundle-hacker-5.0.0.sha2
Desktop $ solo program aux enter-bootloader
Solo rebooted.  Reconnecting...
Traceback (most recent call last):
  File "/usr/local/bin/solo", line 8, in <module>
    sys.exit(solo_cli())
  File "/usr/local/lib/python3.9/site-packages/click/core.py", line 829, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/lib/python3.9/site-packages/click/core.py", line 782, in main
    rv = self.invoke(ctx)
  File "/usr/local/lib/python3.9/site-packages/click/core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python3.9/site-packages/click/core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python3.9/site-packages/click/core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python3.9/site-packages/click/core.py", line 1066, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/lib/python3.9/site-packages/click/core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/lib/python3.9/site-packages/solo/cli/program.py", line 219, in enter_bootloader
    return _enter_bootloader(serial)
  File "/usr/local/lib/python3.9/site-packages/solo/cli/program.py", line 206, in _enter_bootloader
    if solo.client.find(serial) is None:
  File "/usr/local/lib/python3.9/site-packages/solo/client.py", line 53, in find
    raise solo.exceptions.NoSoloFoundError("no Solo found")
solo.exceptions.NoSoloFoundError: no Solo found
 Desktop $ solo ls
Not using FIDO2 interface.
:: Solos
208B31985653: Solo Bootloader 5.0.0
 Desktop $ solo program aux enter-bootloader
Not using FIDO2 interface.
Solo rebooted.  Reconnecting...
Not using FIDO2 interface.
 Desktop $ solo program aux enter-dfu
Not using FIDO2 interface.
Please powercycle the device (pull out, plug in again)
 Desktop $ solo program aux enter-dfu
Traceback (most recent call last):
  File "/usr/local/bin/solo", line 8, in <module>
    sys.exit(solo_cli())
  File "/usr/local/lib/python3.9/site-packages/click/core.py", line 829, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/lib/python3.9/site-packages/click/core.py", line 782, in main
    rv = self.invoke(ctx)
  File "/usr/local/lib/python3.9/site-packages/click/core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python3.9/site-packages/click/core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python3.9/site-packages/click/core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python3.9/site-packages/click/core.py", line 1066, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/lib/python3.9/site-packages/click/core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/lib/python3.9/site-packages/solo/cli/program.py", line 247, in enter_dfu
    p = solo.client.find(serial)
  File "/usr/local/lib/python3.9/site-packages/solo/client.py", line 53, in find
    raise solo.exceptions.NoSoloFoundError("no Solo found")
solo.exceptions.NoSoloFoundError: no Solo found
 Desktop $ solo ls
:: Solos
...

The "Please powercycle the device (pull out, plug in again)" is important

I still see the BOOTLOADER in lsusb:

Bus 020 Device 024: ID 0483:df11 STMicroelectronics STM32 BOOTLOADER Serial: 208B31985653

The firmware worked!
solo program dfu bundle-hacker-5.0.0.hex

$ solo program dfu bundle-hacker-5.0.0.hex
erasing...
downloading 100.00%  08038800 - 0803882e ...         
time: 5920 ms
verifying...
reading 100.00%  08038800 - 0803882e ...         
firmware readback verified.

$ solo program aux leave-dfu
Rewriting option bytes...
Warning: OSError with write_page
Please powercycle the device (pull out, plug in again)

$ solo ls
:: Solos
208B31985653: Solo DiceKeys 5.0.0
$ solo key verify
Please press the button on your Solo key
Register valid
Solo Hacker firmware.