2016 – Office Web App not only works for Excel

There are 4 web applications available in our SP2016 on-prem environment. In all web applications, the Office Web App does not work only for Excel files. Word / PPT files can be easily opened with OWA. UAT and Prodution use the same OWA server, and this behavior is the same in UAT and in production. How can this issue be resolved or remedied?

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