[66fm472tjy7]

I cannot confirm this behavior. With a router running FRITZ!OS:7.57 configured to use Google's DNS (in the router only) I get the following on Windows 10

  > nslookup google.com
  Server:  fritz.box
  Address:  fd00::[redacted]

  Non-authoritative answer:
  Name:    google.com
  Addresses:  2a00:1450:4001:828::200e
            142.250.181.238

Update: the connection does have the DNS suffix, so according to the superuser answer linked in OP (which is the first result when looking up what a DNS suffix is), it should get appended to lookups on windows, but it looks like it isn't in my case.

  > ipconfig
  [...]
  Connection-specific DNS Suffix  . : fritz.box

[mmcnl]

I noticed a lot of comments explaining the same thing, but also some confirming my observations. So far it appears the issue is mostly present if you have configured a separate DNS server in the DHCP settings, e.g. DNS is resolved somewhere outside the Fritz!Box. I will investigate further and update the article.