@Richard Barraclough
Thanks for clarification as i can see, Azure App service deploy task has no updated task version: https://learn.microsoft.com/en-us/azure/devops/pipelines/tasks/reference/azure-rm-web-app-deployment-v4?view=azure-pipelines
You could consider adding an Azure CLI task to your flows with the following command:
az webapp config set -g <resource-group> -n <app-service-name> --linux-fx-version “DOTNETCORE|8.0”
Doc reference: https://learn.microsoft.com/en-us/cli/azure/webapp/config?view=azure-cli-latest#az-webapp-config-set
Also, For Azure DevOps suggest you please post your question here and experts will guide you https://developercommunity.visualstudio.com/spaces/21/index.html
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