@radzmarcorrectly states that XFA based, interactive PDFs cannot be displayed in modern browsers. And there is no "Save them in another way" that will resolve this issue.
Depending on your use case you may revise the existing XFA templates to be saved as flattened PDF. Scripting can be executed in both contexts - but may happen in differernt events. Flattening or print rendering require your scripts not to be placed in client only events (exit from field for example) and they have to be executed "server-side".
If you need to use these documents in future you will not get around a migration of your existing templates from interactive PDF to static PDF.