Currently there is a limitation of uploading a file attachment size to max of 10 MB. SInce SPO can accept upto 250 MB per file in a list item, it makes sense to increase the attachment size in PowerApps to 250MB.
this is a deal breaker for one of my customers and they will have to use another solution. It is very dissapointing that this basic functionality has not been improved while other new features that provide very little value have been added.
Please see page 2 of the comments. As @FilipK mentioned, the team is working on coming up with a date. Annoying as can be, but that's all we have right now.
We are increasing the upload limit to 100MB but the planned October release date is in jeopardy. Still aiming for this year, I will update the thread.