Allow cellular data switching not working.

I have turned on “Allow cellular data switching” and have two sims in my phone. One esim and the other is a physical sim. “Allow cellular data switching” isn’t it supposed to switch automatically? I mean I have data plans on my both sims. So, is it supposed to switch if one runs out of data, or unable to connect to cellular data ? In my case it not switching when one runs out of data. Or the case is that it solely depends on cellular signal strength? If it depends one data connectivity then how should I fix that?