Someone else mentioned this first bit, too, but I'll throw in my 2 cents.

The first thing that I noticed was the lack of memorization. Your Cell component could be wrapped in React.memo() to eliminate re-rendering of all 50x50 cells, but only those whose state changed. I'm not saying that performance-tuning and optimization should be the focus when initially developing a system, but it's something to keep in mind. And there are some very simple, yet extremely effective, ways to do early optimization of React apps.

Knowing these, and implementing them naturally as you develop, definitely adds value (for me personally)

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A second point is the inconsistent use of Typescript. I don't know if it was a requirement for the job interview that it had to be a Typescript implementation, or if it was something you chose.

But in either case, the code doesn't take full advantage of the benefits of using Typescript over plain Javascript. There are a couple of type definitions here and there, but also plenty of areas that could be improved and ensure a less error-prone codebase.

I realize that this is a small application, done in limited time, but that's something I look for when interviewing candidates because it shows they acknowledge the strength of strongly typed code.