In the Azure Functions Flex Consumption plan, how can we get the current/instant instance count for a Function App?

In the Azure Functions Flex Consumption plan, how can we get the instance count both in real time and for a specific point in time?

We would like to:

See how many instances are currently running in real time.
Check how many instances were running at a specific historical time, especially during high message volume or scale-out events.

Is there a recommended way to get this information through Azure Portal, Application Insights, Live Metrics, Azure Monitor metrics, or KQL?

No repository file, test, or code entry point is identified. Start by comparing Azure Portal, Application Insights, Live Metrics, Azure Monitor metrics, and KQL for current and historical Flex Consumption instance counts. Done means documenting a supported way to obtain both values, or clearly stating the limitation if one is unavailable.

Written by the indexing model from the issue text.