1. *Use Azure CLI*: You can create a Web App with .NET 6 using the Azure CLI command:

```

bash

az webapp create --resource-group <resource-group-name> --plan <app-service-plan-name> --name <web-app-name> --runtime "dotnet:6"

```

Replace `<resource-group-name>`, `<app-service-plan-name>`, and `<web-app-name>` with your actual values.

2. *Use Azure PowerShell*: You can also use Azure PowerShell to create a Web App with .NET 6:

```

New-AzWebApp -ResourceGroupName <resource-group-name> -AppServicePlanName <app-service-plan-name> -Name <web-app-name> -Runtime "dotnet:6"

```

Again, replace the placeholders with your actual values.

If you're stuck with the portal, you can also try to use the "Code" or "Docker" option and specify the .NET 6 runtime manually.

Regarding whether to stay with .NET 6 or upgrade to .NET 8 (LTS), consider the following factors:

- *Support lifecycle*: .NET 6 as reach its end-of-life on November 12, 2024. .NET 8, being an LTS version, will have a longer support period (until November 2026).

Ultimately, the decision to stay with .NET 6 or upgrade to .NET 8 depends on your application's specific needs, dependencies, and your team's expertise.