Because it was not a straightforward search including superuser and reddit:
Chrome: C:\Users\<user>\AppData\Local\Chrome\User Data\Default\Local Extension Settings\chphlpgkkbolifaimnlloiipkdnihall
Brave: C:\Users\<user>\AppData\Local\BraveSoftware\Brave-Browser\User Data\Default\Local Extension Settings\chphlpgkkbolifaimnlloiipkdnihall
“chphlpgkkbolifaimnlloiipkdnihall’ being the OneTab extension.