"winbind:ignore domains" stopped working a while ago due to the commits that removed the parameter "map untrusted to domain" in Samba 4.8 cf commits 443984b8 and especially e7bc23e4.
As a side note, even in older version "winbind:ignore domains" was only effective for NTLM authentication. The NTLM auth code uses the trusted domain list as part of the code the implements "map untrusted to domain" and this is the part where auth will fail is a domain is blacklisted.