I have the domain tl-photography.at.
I changed the NS records and could verify this here: https://dnschecker.org/ns-lookup.php?query=tl-photography.at&dns=google
But Cloudflare still can’t verify my domain.
Any ideas what I could do?
PS. I change the NS records on the weekend, so plenty of time to propagate.
You appear to have created NS records in your DNS zone at ns1.nameservice.at and ns2.nameservice.at. That is not how you add a domain to Cloudflare.
You need to replace the ns1.nameservice.at and ns2.nameservice.at nameservers at your registrar with those assigned by Cloudflare, presumably ada.ns.cloudflare.com and roan.ns.cloudflare.com, but best to copy and paste from your Cloudflare dashboard. https://dash.cloudflare.com/?to=/:account/:zone/dns/records
I have changed the NS entires at my registrars DNS settings.
How can it be that whois on CMD shows the old entries, while https://dnschecker.org/ns-lookup.php?query=tl-photography.at&dns=google shows the entries I have got from CF?
You are changing the NS records in your zone, tl-photography.at.
When you update the nameservers at your registrar as required, the nsameservers for tl-photography.at. are updated in the parent nameservers for the at. zone.
Let’s ask the internet for the NS records for at. and ask one of them for the nameservers for tl-photography.at. to help you understand why what you are doing is not working.
https://dnsviz.net/d/tl-photography.at/dnssec/ gives me two warnings:
at to tl-photography.at: The following NS name(s) were found in the authoritative NS RRset, but not in the delegation NS RRset (i.e., in the at zone): roan.ns.cloudflare.com, ada.ns.cloudflare.com
at to tl-photography.at: The following NS name(s) were found in the delegation NS RRset (i.e., in the at zone), but not in the authoritative NS RRset: ns1.nameservice.at, ns2.nameservice.at