I read your original post. You have issue 30 seconds reboot. so I assume your dongle FW is before 2021.Jan.28.
and you could do OTA updating several times even though it is failed. so Dongle itself is not broken.
I'm not sure 30 seconds reboot issue affects OTA updating. Just in case, To prevent 30 seconds reboot issue during OTA updating, I suppose USB updating should be used. but it is never succeeded with USB. This is my understanding of your situation.
1. Plug the dongle to wall charger without USB. Normally LED will be solid RED color after 5 seconds. Is your dongle same ?
2. Plug your USB into dongle (Don't plug off the dongle from wall charger. Just plug USB into dongle), Normally LED will be flashing red and green., and don't touch anything until solid red +2 minutes if flashing.
Above 1 and 2 are my dongle LED.
If you stored 2021.03.06 FW on your USB, How about if you stored 2021.Jan.28 FW ?
At least, Many of Mazda user could resolved by 2021.Jan.28 FW even though we had issue 30 seconds reboot.