Flatpaks also just come with a set of default permissions at install time, so running in a sandbox only really protects against flaws in the software, but not against malicious intentions by its creator. Flatpak doesn’t have an “ask for permission” system afaik, at least not standardized. What you do is you add or subtract from the default the app itself specifies.
Input latency for one, because the next frame is delayed where the interpolated frame is inserted.
And image quality. The generated frame is, as I said, interpolated. Whether that’s just using an algorithm or machine learning, it’s not even close to being accurate (at this point in time).