> At least on Linux, isn't DNS all at the application level anyway? There is no system level DNS lookup
Nearly all applications use the standard library, i.e. getaddrinfo(3) or the old gethostbyname(3) or something that wraps them. Which itself uses the services configured in /etc/nsswitch.conf, one of which is DNS which will in turn query the DNS server(s) configured in /etc/resolv.conf.
You can also have other services configured in nsswitch.conf like "mdns" (multicast DNS for names of devices on the LAN) and "files" for /etc/hosts, or any other name resolution system. The general result is that you can change the settings for the whole system and even add completely new name resolution services (like, for example, DoH) and have substantially everything automatically use them.
Nearly all applications use the standard library, i.e. getaddrinfo(3) or the old gethostbyname(3) or something that wraps them. Which itself uses the services configured in /etc/nsswitch.conf, one of which is DNS which will in turn query the DNS server(s) configured in /etc/resolv.conf.
You can also have other services configured in nsswitch.conf like "mdns" (multicast DNS for names of devices on the LAN) and "files" for /etc/hosts, or any other name resolution system. The general result is that you can change the settings for the whole system and even add completely new name resolution services (like, for example, DoH) and have substantially everything automatically use them.