DHCP on LibreELEC 12.0.2 with connman (2.0) and iw (6.17) versions from master works.
I had to patch some checksums and I've also pulled in iwd (for good measure) and nftables (marked as dependency of conman in master branch) along with a newer version libnftnl (needed by nftables). If anyone is interested, my I've pushed my changes to a separate branch in my fork.
I'll (try to) test 12.0.2 kernel/drivers on master/nightly next.