Hi, @PedroSoares-4915 ,
If you goal is to use the web part only for classic pages, no need to change the web application. In SharePoint 2019, we can create both team site (classic) and modern team site under the same web application. There is no settings limit a web application to only allow modern sites.
Plus, under a modern team site, you can still create a classic page like web part page or wiki page. Just go Site Contents> Site Pages> New button , then you can choose a web part page or wiki page. They are classic pages supporting classic web parts like Reporting Services Viewer web part.
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