EDIT: actually not ZModem, but it supports X/YModem -- source code, despite the comment at its beginning, finally says "Sorry, zModem not available yet"

yes and also X/Ymodem, see source code: https://elixir.bootlin.com/u-boot/latest/source/common/xyzMo...

extremely useful feature (I used xmodem in the past, if I remember well)

Did not know that. Indeed it's very useful. Thank you!