The majority of mobile phone eSIM/SIM,cards are not correctly provisioned for use with tablet computers. If they work at all, they may not provide access to the full range of cellular services. This is not a limitation of the iPad, but of the Cellular network provider.
If using an eSIM or physical SIM with iPad, you will require a DataSIM explicitly provisioned for iPad or mobile broadband (a.k.a. MiFi).
Be aware that an iPad, whether a Cellular model or not, is not capable of directly accessing Cellular Voice or SMS/MMS Messaging features. An iPad with either WiFi or Cellular connectivity alone can only access IP-data services. If you have added an eSIM or a DataSIM and Cellular plan to a WiFi+Cellular model of iPad, the number associated with the SIM card is only used to identify your account for billing purposes. This number is not used for making calls or sending messages.