Upgrading Netgear WNDR3700 V4 from 18.06.1 to 21.02

Hello,

I was following the instructions at Netgear WNDR3700v4 not booting anymore after upgrading to 21.02.01 - #2 by hnyman to no avail.
Tried tftp flashing to any of openwrt 21.02.x but it was just boot looping.
Flashing to openwrt 19.xx and stock firmware works fine.
Finally I used nmrpflash to flash openwrt 21.02.2, 21.02.1, 21.02.0 and it's still boot looping.

What to do, what to try?

Thanks!