Hello,
I have same problem, I did rollback my carlinkit 4.0 plugged into car (sic! don't do that! ) had power loss and my device died (no red nothing). Now I have red light by instruction from
https://github.com/ludwig-v/wireless-carplay-dongle-reverse-engineering I put MX25L12835F_CFW_20210830.bin file by ch341. Yes I know its v3 file, when I put into usb file U2AW_AUTOKIT_Update there's nothing (green red led) only red, but if I put file U2W_AUTOKIT_Update there is (red green for ~1minute) but still hardware error:wifi bt after pluged into car. I tried everything change file name, another firmwares img, bin files nothing. Probably need v4 .bin file into mx25L12835F solve this problem but I can't get this. Support send me only U2AW_AUTOKIT_Update.img file. Anyone help?