EasyHook VS Magpie

Memory manipulation can be done very easily by pinvoking Read/WriteProcessMemory(), but it's not really fun nor very powerful, you'll almost always need to hook some function, and for that you'll need some form of binary patching or DLL injection. The latter is not practical to do in C# because it depends on the CLRuntime, which would require a loader written in a lang like C++ anyway (take a look at this dead project). Idk any tutorials but take a look at Frida.re, Ghidra and maybe CheatEngine.

Example: https://github.com/EasyHook/EasyHook/issues/16

depending on the game, fsr(or dlss if you have the option) may be available in options to help you out, otherwise you could give a free option a go, such as Magpie

For games that won't go full screen, at least we have Magpie as a last resort. The experience won't be as seamless though...

Another thing you can try is playing the game in a borderless window at a lower resolution and using Magpie to upscale it to fullscreen. Magpie offers a variety of upscaling options that can produce a less blurry image than the bilinear interpolation that is typically done when upscaling by the GPU or display.

Configure VLC to play the video in an extra window with the same resolution as the video source and upscale the window to fit the screen. On Windows 10 the FSR upscaling can be achieved with Magpie. On the Steam Deck the system built-in FSR/CAS combination is used.

Something else that may also be of interest is Magpie. It's a tool to upscale windowed content into fullscreen with a variety of upscaling methods available.

also using enabled antialiasing in game settings (or even globally set in video driver) consume much less resources then rendering full size bigger resolution image for reducing aliasing. there are also such tools like Magpie (https://github.com/Blinue/Magpie/blob/main/README_EN.md) or Lossless Scaling tool from Steam. they enable FSR supersampling to any game on any GPU.

https://github.com/blinue/magpie https://store.steampowed.com/app/993090/lossless_scaling/

To everything that the community has said, I also want to add that No Man's Sky has FSR tech (the game runs at a lower resolution and it's upscaled). You can use Magpie or even better, Losless Scaling to create a similar effect in SC and win some extra frames :)