HKEY_LOCAL_MACHINE\SYSTEM\Internet Communication Management\Internet Communication.
Apparently it's a Pro edition key used for editing a group policy, but can I add it to Home edition (version 1903)?
*edit: Moab helpfully pointed out that instead of adding one group-policy-editable key to the registry, it's possible to add the entire GPO functionality to Home edition. If/when I try this I'll update this question. The bigger question (and its answer) are linked in his comment below.