The file size for uploading PPTX files is regulated by the backend and is 500MB by default.
Since the version of the empower backend 1.0.0600.0064 it is possible to configure this limit.
Usually set in: appsettings.json. This can be found in the PPTX API configuration directory under the following path: (from 8.6) %ProgramData%\empower\backend\empower\root\Services\CoreAPI\appsettings.json
(to 8.5) %ProgramData%\Made in Office\empower backend\empower\root\Services\CoreAPI\appsettings.json
You can copy and paste these into your Windows Explorer line (make sure you have replaced the environment name).
"MaximumFileSize": "524288000" //DefaultValue: 500MB
To ensure stable operation of the backend, we recommend at least 16GB of RAM for an upload limit above 500MB.