If there is grain in the source original, then a “cleaned” version is not an archival copy in my opinion. Grain is difficult to compress as it is random noise, so the bitrates required to maintain it are high.

If you see grain in a movie then it is meant to be there.

Film CAN look crystal clear and modern, but it also has flaws that show depending on how it is used and what film is used in the first place. if you start with high ISO film and push it in development it will have serious grain, but low ISO film fully exposed and well developed can be as smooth as glass, even on a 4K scan, problem is you have to have a huge amount of light to get film to look that clear and sometimes that isn’t possible. you can get around some of this with day-for-night methods (filming fully lit then darkening to look like night) but that is a choice the director/DOP make in a production.

Digital cameras have grain too, and it can be much uglier than film grain but our modern image sensors can handle low light better than film (in some ways, it’s a debate still) but even clear, well lit, well exposed, low ISO digital video productions will have grain added to tie scenes together visually if lighting changes slightly, to mask flaws, and to tie composites together (mixing cg and video for example). Small amounts of grain can actually enhance apparent detail as your brain fills in what it perceives as detail, Sony TVs can do this as part of their upscaling if you enable it.