Just as deHakkelaar, I have no problems resolving deutsche-glasfaser.de through that IPv4.
185.22.45.49 is the IPv4 of one of Deutsche-Glasfaser's DNS servers, dnsauth002.dg-w.de (another is dnsauth001.dg-w.de).
~$ nslookup dnsauth002.dg-w.de
Server: 192.168.178.28
Address: 192.168.178.28#53
Non-authoritative answer:
Name: dnsauth002.dg-w.de
Address: 185.22.45.49
Name: dnsauth002.dg-w.de
Address: 2a00:6020:200::2
What does above nslookup return for you?
As that server IP is answering DNS requests from certain networks (as deHakkelaar's, DL6ER's and mine), it would seem that either your ISP blocks access to 185.22.45.49, or that DNS server is rejecting requests originating from your ISP's network IPv4 address range.
The latter would definitely be a misconfiguration of Deutsche-Glasfaser's DNS resolution chain: 185.22.45.49 shouldn't be provided as authoritative DNS server if it cannot properly handle DNS requests.
If your network would have public IPv6 connectivity, could you try to resolve through dnsauth002.dg-w.de's IPv6 address (maybe their IPv6 server is configured correctly):
dig +norecurse @2a00:6020:200::2 deutsche-glasfaser.de.