ns2.proton.ch has no CNAME records.
Question and response
Question
dig ns2.proton.ch. NS
Answer
The response has no answer records.
Authority
proton.ch. 718 SOA ns1.proton.ch. support.proton.ch. 2026030306 1200 144 1814400 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0