@Shawn Thank you for reaching out to Microsoft Q&A, apologize for any inconvenience caused on this.
Based on the shared information, looks like you are trying to create a connection file system
using built-in connector as mentioned in the error message that file system built-in connector is supported only for App Service Environment v3 with Windows plans only.
Please make sure that your app service is under the windows plan and supported for logic app pricing tier: Usage metering, billing, and pricing - Azure Logic Apps | Microsoft Learn
You can connect to the on-prem file share which are in same virtual network directly without using on-prem gateway which is explained in this documentation here as well.