Based on your question, let me try to explain how IIS manage the connections. Basically the following parameters affect the connections.
The maximum requests that can be handled by your IIS will be determined by IIS maximum number of concurrent worker threads / Maximum number of concurrent connections. If the concurrent requests are more than those values defined, then IIS need to queue the requests. The Queue length defines the number of request that will be queued by IIS and the remaining requests will be sent with 503 status code.
https://learn.microsoft.com/en-us/dotnet/api/microsoft.web.administration.applicationpool.queuelength?view=iis-dotnet
https://learn.microsoft.com/en-us/answers/questions/585468/maximum-connection-limit-in-net-frame-work-47.html
Hope this helps