One piece of hardware I periodically search the internet for, is a CRT emulation box. I want a piece of physical hardware I can place between my 4-port RCA switcher, and an HDMI connected modern TV, that emulates the display properties of a CRT.
I know that a real CRT would be the best for my nostalgia vibes, but honestly they take up so much space. This theoretical product doesn't need to be perfect, just give me a few knobs to turn to adjust whatever settings are available, and inject vertical bars to fix the aspect ratio. I'd pay good money for such a device.
It does all of what you ask, plus a lot more. CRT filters that emulate CRT shadow masks from different manufacturers, HDR to boost the max brightness to emulate the phosphor glow, VRR to allow for arbitrary refresh rates (useful for arcade superguns).
Just to save folks a whole click or two, it's $750 which does seem ... steep but I'm not into retro computing (yet, a part of my brain feels like adding). I've heard it mentioned on Youtube ("8-bit guy", I think) but never looked it up, thanks GP.
Here's my 2 cents: no one needs that kind of stuff. Retro can be free, and only reason you would want to break out your wallet is if you really care that much about things beyond the game.
As I understand, the OSSC Pro is significantly cheaper for most of the feature set, while the RT5x and OSSC provide varying feature sets (the OSSC only has a line buffer, not framebuffer, which affects the resolutions it can output).
You're not wrong that's the OSSC Pro has most of the same feature set, but that deeply undersells the headline feature the RT4K has, particularly given the OP wants something that properly emulates the visual characteristics of a CRT. For that, it's impossible to beat the RetroTINK 4K. Matched with a 4K OLED it's CRT shaders are uncannily real looking.
I know that a real CRT would be the best for my nostalgia vibes, but honestly they take up so much space. This theoretical product doesn't need to be perfect, just give me a few knobs to turn to adjust whatever settings are available, and inject vertical bars to fix the aspect ratio. I'd pay good money for such a device.