Comment 2 for bug 1804648

host.c does have "U": https://github.com/isc-projects/bind9/blob/master/bin/dig/host.c#L793

it's even in the optstring array: https://github.com/isc-projects/bind9/blob/master/bin/dig/host.c#L588

But the pre_parse() function in https://github.com/isc-projects/bind9/blob/master/bin/dig/host.c#L597 isn't handling it

I think this ought to fix it:
--- a/bin/dig/host.c
+++ b/bin/dig/host.c
@@ -657,6 +657,7 @@ pre_parse_args(int argc, char **argv) {
                case 'N': break;
                case 'R': break;
                case 'T': break;
+ case 'U': break;
                case 'W': break;
                default:
                        show_usage();

I'll give it a try and submit upstream if it works.