You can find STYLY's official size limits here https://styly.cc/manual/unity-asset-uploader/#:~:text=The%20maximum%20file%20size%20is,have%20set%20a%20recommended%20size.
-Uploading a Prefab is recommended to be less than 20MB.
-Uploading a Scene is recommended to be less than 100MB.
-The maximum upload size from Unity using *AzCopy is 512MB.
-256MB when not using AzCopy from Unity
-Maximum file size is 100MB when using the model upload function on STYLY Studio
Keep in mind that you should test your scene on a HMD and in the browser if its VR and on a mobile device if its AR. Sometimes a scene that's under the limit will still be too computationally intense for some devices. In general its better to air on the side of optimization so that your content is accessible to as many people as possible.
I'm working on a project in Unity and I'd like to know what the maximum file size is if I'm planning on uploading to STYLY. Is it different for scenes vs prefabs?