Windows 10 service called AarSvc_70f961. What is it and how could I disable it?

It's possible to set this service to disabled. Open Regedit, and navigate to:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\AarSvc_70f96

Note that the trailing five digits will be different on every system. They can be determined by checking the "Service Name" entry shown when you double click on the service entry in the Services MMC plugin.

Inside that key is an entry "Start" which is a 32 bit DWORD value. Set that value to 4, the service will be disabled, and will not start at boot time.

You will also see another service AarSvc immediately above the one with the five digit random number. According to this page: https://docs.microsoft.com/en-us/windows/application-management/per-user-services-in-windows services of this sort are Per User services, and to completely disable them, the version without the five digits, AKA the template service, should also have its "Start" value set to 4.

Reading over this Microsoft page, it seems this service relates to digital Assistants, such as Cortana and how they use the Windows.ApplicationModel.ConversationalAgent Namespace that appears to have been added in Windows 10 version 1903 (see the "Develop Windows Apps" section).

Provides applications the ability to expose functionality through any digital assistant supported by the Windows platform Agent Activation Runtime (AAR).

I don't see any reason to disable it, but in the one link you provided in your question, one of the dependencies of this service is Windows Audio. If this service is stopped or disabled, the Agent Activation Runtime service will be unable to start according to that page:

Agent Activation Runtime is unable to start, if the Windows Audio service is stopped or disabled.

I wouldn't recommend stopping Windows Audio however, as that will probably lead to a lot of unwanted issues.