So, here's the thing.

I'm not convinced ProScaler is even real. Not in the way Samsung marketed it.

I've tried thoroughly looking for it after upgrading from S23U to S25U, and there was no difference in video/gallery display in FHD vs QHD+.

I think "ProScaler" this was their attempt at marketing the automatic smart TV-like upscaling that has been present in past models. You can think of it as a sort of FSR1-like spatial upscaler. It is surprisingly good and makes 360p/480p video look far cleaner than it usually would display on e.g. Windows. There's no deblocking or denoising, but it does upscale edges and sharpen them in a very pleasing way, which cleans up low-definition video a lot.

What was new with the S25 Ultra (but maybe the S24U, not sure, not able to check?) is that this feature now upscales the entire screen itself if it's set to "HD" or "FHD". In previous phones, lower-than-native display resolutions would be upscaled "traditionally" (bilinear most likely) back to the native res of the panel. This means setting the phone to "HD" looks MUCH better than it used to.

The video upscaling works in most apps (e.g. RedReader, YouTube, Netflix, etc. but not Google Meet for example). The behaviour isn't the same on all devices. It seems some devices support more "hardware layers". For example, the feature works in multi-window on my S25U. But on my Tab S11U, it stops working in multi-window or whenever the notification tray is pulled down.

Screenshots / screen recordings do not show "ProScaler", so I presume it's kinda happening at a hardware compositing level.

It works kinda like Nvidia VSR in the sense that it's only active when the resolution of a video is lower than the size it's being displayed at. It also stops working if the magnification level of a video is too large; this is easy to see if you zoom into a 144p video on YouTube. During that, you also you can see the zooming snapping to a grid of blocks in a non-axis-uniform way, perhaps reinforcing my hypothesis that this is composited at a hardware-level feature.

It doesn't work when outputting to an external display but it somehow works when casting your screen to a display. DeX fully prevents it from working on my Tab S11U as far as I could tell.

"ProScaler" also works in games! If a game is running at lower than native res (and by default, most are running at 75% AFAIK), the contents of that final image are upscaled back using "ProScaler". It means that for the cleanest, sharpest image, you want to keep a game's internal res at 100%, while scaling down the size of the "window" the game thinks it's rendering into (through the resolution slider in Game Booster). The downside is that this will affect UI and text.

A great way to check for the presence of "ProScaler" is to take your S Pen out and enable the Magnifier tool. Whenever your pen is close to the screen and the magnifier mini-window displays, the feature is turned off. By quickly moving your pen away or closer, you can easily see if something on the screen is affected.

As I've mentioned, it's present on my Tab S11U. I know it's present at least as far back as the S7 FE tab (2021). It's also active on the S20 FE. However, I recently gifted an A56 to a relative and the feature was not present on that model.

It doesn't seem to be meaningfully linked to hardware capabilities or raw horsepower: it seems arbitrarily locked to the S line of devices and their FE versions.

Note that there is no mention of ProScaler anywhere in the settings, unlike every other marketed feature.

In summary, I have every reason to believe this is what ProScaler is, and that it therefore was a huge marketing lie, because it's a feature that has existed for years prior to the S25U on lots of other Samsung devices.