iPad pro cellular is not showing the cellular antenna icon anymore

You might be well advised to seek assistance directly from from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page.

Alternatively and perhaps easier, you can initiate and manage your support cases using the excellent Apple Support App. If not already installed on your iPad, the App can be downloaded from the App Store:

https://apps.apple.com/gb/app/apple-support/id1130498044

Do you still have an active (paid) cellular service agreement? iPadOS will only show Cellular settings when you have an active physical SIM or eSIM; if don’t have an active Cellular service contract, Cellular settings will not be accessible.

Early iPad Pro models also supported AppleSIM. This service, created by Apple and partnered by selected Cellular Providers, was closed earlier this year for new service activations. With closure of this service, iPadOS has been updated to remove associated settings and references - and this may impact what you see when you don’t have an active Cellular service plan with a Cellular Provider.

Thanks for clarification.

A reset of your iPad network settings may be helpful - as this will reset both Cellular and WiFi network settings:

Settings > General > Transfer or Reset iPad > Reset > Reset Network Settings

After performing the Network Reset, check for a Carrier Settings update:

Settings > General > About > Network Provider - ???

The No SIM indication should only be seen if you don’t have a physical SIM installed - and your eSIM has not been provisioned.

In most cases, a regular mobile phone SIM cannot be used with iPad. Most Cellular Carriers instead supply a Data-SIM, these being configured with appropriate services enabled.