A server maintains tens of thousands of connections simultaneously but only few hundreds are sending and receiving data at the same time

I need to make a web server that maintains tens of thousands of connections simultaneously, but only few hundreds are sending and receiving data at the same time.

I need to keep this connections active as I need to send notifications to them but I can't use websockets.

The questions are:

Is this a bad design or keeping many connections simultaneously without transmitting data doesn't need much resources?

Will the performance be bad?