We have used some austrian and german DNS Proivder (easyname.at, hetzener.de, …) but a lot of them does not offer DNSSEC. We are now on OVH but they are quite slow when a change happen via there Interface. Have anybody another european DNS Provider which supports DNSSEC in combination with deSEC?
As far as I have understood is deSEC not a DNS Provider where you can buy domains, right?
I have been using https://www.inwx.de for years. Since domains are their core business, I trust that it will work. But there are certainly dozens of different recommendations…
but they are quite slow when a change happen via there Interface
Not sure if you mean the interface or the change in DNS. If the latter, keep in mind that DNS changes are not registrar dependent. The registrar just passes it on to the registry, and depending on the Registry/TLD there are different TTLs and the zone is reloaded differently often.