This is for the official Google Chrome. No idea how Chromium works - it depends on your distro. The policy files are most likely compatible with Chromium forks as well but again the policies directory will be different.
To be put into /etc/opt/chrome/policies/managed:
DoH.json:{ "DnsOverHttpsMode": "secure" }
DoH-server.json:{ "DnsOverHttpsTemplates": "https://one.one.one.one/dns-query" }
ExtensionManifestV2Availability.json:{ "ExtensionManifestV2Availability": 2 }
Files names are totally arbitrary.