I believe you can query this information from your server/cloud by following these instructions https://docs.mendix.com/refguide/monitoring-mendix-runtime#server-statistics
The number of HTTPS connections should be unlimited, but the number of threads that are simulatnously running to process those reuqests is limited. If you want to increase the maximum number of threads you need a good CPU and a good amount of RAM.
Finally, you should also think about increasing the number of database connections available (by default 50) read more here - https://docs.mendix.com/refguide/custom-settings#connection-pooling
Hope this helps,