Hi @valerian
The domain digi-stud.io
has DNSSEC turned on.
$ whois digi-stud.io | grep DNSSEC
DNSSEC: signedDelegation
As per this documentation Netlify does not support domains with DNSSEC (there is a fetured request here; also see this thread.)
If you wish to use Netlify DNS you will need to turn off DNSSEC at the registrar. Alternatively, you can use external DNS and retain DNSSEC on your domain.