There is a default single file size upload limit of 10 MB in Power Apps Portal with SharePoint Online integration. This can be configured to 50 MB. I have explained how to make the change on this post.
If you are coming from CRM world, probably it is an easy change on the Power Apps Portal. However, if you have never used CRM system there is no instruction on how to make this change. There is only one sentence in Microsoft documentation, which does not make sense if it is your first time configuring Power Apps Portal.
1- Navigate to Portal Site Settings
To navigate to portal site settings you can either go to Portal Management App then Site Settings. You can also click on Portal Settings and select “Site settings” from the right drawer window.
2- Insert new settings
Make sure Site Settings is selected on the left navigation then click New from the top menu.
Type on the Name exactly SharePoint/MaxUploadSize, choose your portal for Website field and type 50000 (in KB) on the Value field. You can also type some descriptions. Finally, click “Save & Close” and you might need to refresh the cache for your Portal and the settings should take effect immediately.