Thanks for the article. It is nicely explained.
I am facing the same issue with APIM after adding UDR pointing to Azure pipeline, that API's do not load and receive an error "Failed to connect to management endpoint servicename.management.azure-api.net:3443 for a service deployed in a Virtual Network. Make sure to follow guidance at https://aka.ms/apim-vnet-common-issues.management endpoint."
I have ensured that the NSG has inbound and outbound rules set as mentioned in this article and have added routes - global and region speicific ip address with destination as internet and 0.0.0.0 pointing to the Azure firewall in UDR (https://techcommunity.microsoft.com/t5/azure-paas-developer-blog/api-management-networking-faqs-demystifying-series-ii/ba-p/1502056).
Please suggest.