I tried the firmware update command via Dietpi-config.
And in addition, this command.
https://dietpi.com/forum/t/firmware-bootloader-update-raspberry-pi-4/5426/4
I always have after a reboot :
root@DietPi:~# rpi-eeprom-update
*** UPDATE AVAILABLE ***
BOOTLOADER: update available
CURRENT: Thu Apr 29 16:11:25 UTC 2021 (1619712685)
LATEST: Mon Nov 22 11:23:32 UTC 2021 (1637580212)
RELEASE: latest (/lib/firmware/raspberrypi/bootloader/latest)
Use raspi-config to change the release.
VL805_FW: Using bootloader EEPROM
VL805: up to date
CURRENT: 000138a1
LATEST: 000138a1
If I try "rpi-eeprom-update -d -a ", it does not work (missing xxxd ??)
[UPDATE]
After reinstalling, update and install the latest version of eeprom (with apt-get install xxd).
Everything is ok… but the “lsusb” remains empty with dac connected (with USB validate) ! 
root@DietPi:~# rpi-eeprom-update
BOOTLOADER: up to date
CURRENT: lun. 22 nov. 2021 11:23:32 UTC (1637580212)
LATEST: lun. 22 nov. 2021 11:23:32 UTC (1637580212)
RELEASE: latest (/lib/firmware/raspberrypi/bootloader/latest)
Use raspi-config to change the release.
VL805_FW: Using bootloader EEPROM
VL805: up to date
CURRENT: 000138a1
LATEST: 000138a1