CNAME and Enforcing Google Safe Search

[Bucking_Horn]

I've explained that already in my reply to Force safe search using Pi-hole - #2 by Bucking_Horn (your above first link):

@Bucking_Horn

To make CNAMEs work, you'd have to define the respective local DNS records (A and AAAA) for resolution targets as well.
If you consider this, you should be aware that when acquiring the IP addresses to add, the IPs you would receive for resolving a given domain may differ from those that someone requesting it from another geographical location may see.
Also, this approach may break as soon as public DNS resolution of such a target domain would change to a different IP.