Problem with my SharePoint Server 2019

I have installed my SharePoint Server, configured everything, and I can access my server through my browser. However, when I try to open a Word, Excel, or PowerPoint file, the file gets downloaded directly, and I cannot view or edit it online. Strangely, when it's a text file, I can read and edit it. I have tried everything but haven't been able to find a solution. Can you please help me?