How to test application for SharePoint 2019?

Juan is correct that there is not really a way to test his scenario with building an SP2019 environment. Azure is a great resource to build this type of environment for testing, but it's not a trivial undertaking and it does cost. There are ways to get Azure credits to cover this, but remember to shut everything down when you are not using it to minimize the costs. This article is for SP2016, but you should be able to adapt it for SP2019.
https://docs.microsoft.com/en-us/SharePoint/administration/sharepoint-server-2016-dev-test-environment-in-azure

This is an article to build a single VM SP2019 farm for dev/test.
https://synkventures.com/2020/07/07/how-to-install-microsoft-sharepoint-2019-in-azure-virtual-machine-for-demo-labs-or-personal-use/

Disclaimer: I have not tested either of these articles for accuracy. Regardless, they are a good place to start.

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