It's not clear to me if dropping support for this functionality was intentional.

Chain of events:

- #21689 removed test coverage due to a misunderstanding due, I believe, to this functionality being generally supported by all platforms except macOS which does not and returns a different format
- #21756 removed support and caused this regression
- #21690 restores the test coverage that would have caught this regression

Currently, neither the test coverage before #21689 nor the coverage restored by #21690 pass since the merge of #21756.

/**
 * Get the canonical identifier of our network group
 *
 * The groups are assigned in a way where it should be costly for an attacker to
 * obtain addresses with many different group identifiers, even if it is cheap
 * to obtain addresses with the same identifier.
 *
 * @note No two connections will be attempted to addresses with the same network
 *       group.
 */
std::vector<unsigned char> CNetAddr::GetGroup(const std::vector<bool> &asmap) const
{
    std::vector<unsigned char> vchRet;
    uint32_t net_class = GetNetClass();
    
    
    uint32_t asn = GetMappedAS(asmap);
    if (asn != 0) { 
        vchRet.push_back(NET_IPV6); 
        for (int i = 0; i < 4; i++) {
            vchRet.push_back((asn >> (8 * i)) & 0xFF);
        }
        return vchRet;
    }
    vchRet.push_back(net_class);
    int nBits{0};
    if (IsLocal()) {
        
    } else if (IsInternal()) {