This got me thinking about other preventive measures one can take. Protect your keyboard’s keys from fading into oblivion is an older article that proposes using clear, cellophane tape, cutting it to just the size of the individual keys that need more protection. I don’t really like this idea, I think the tape edges could collect dust. The dust could then transfer to the display when closed, not the end of the world but could mean it needs to be cleaned more often.
The article includes a short video, showing someone trying the technique but it also briefly shows another idea that I like more, applying clear nail polish to the keys. I would first try it on an old keyboard you don’t care about, to practice applying it and to see how it feels.
Less DIY are these MacBook keyboard stickers that come in a variety of styles, including transparent. They have a dropdown list of MacBook models, including the 2021 ones, so they should fit.