Yes, physically get bigger. A grown battery by itself isn’t necessarily a problem (they’re designed to grow quite big without bursting) but if something pokes through the shell, like for example sharp electronics, compressed hydrogen gas combined with oxidizing metal can escape through the rupture, turning the battery into a portable flamethrower you can’t extinguish with water (without pincking it up, dunking it in water, and leaving it there for a while).

There’s a subreddit about swollen batteries if you want to see some of the more extreme examples: https://old.reddit.com/r/spicypillows/ In older MacBooks, if the battery inflates, it will push apart the frame of the laptop, making the TouchPad unusable and in extreme cases the frame of the laptop will bulge open.

If the battery becomes a problem, you will notice. If you feel like the chassis is starting to bulge, do NOT press down on it to flatten it, but instead take it to a professional so they can take out and perhaps replace the battery. If you want to do it yourself (possible if you’re careful) make sure to look up guides online; there’s a good chance a big bucket of sand and some basic precautions (goggles, gloves, clothes that don’t ignite easily, etc.) is all you need to do this kind of stuff safely. Batteries are quite safe if you’re not deliberately trying to be stupid with them.

This isn’t just MacBooks either; any lithium battery, including the ones in your phone and earbuds, can swell up. It happens most often during charging, when the battery gets hottest inside, which is why you sometimes see ads telling you not to charge your devices overnight.

All of that said: your laptop isn’t a fire bomb, it’s probably fine. Just don’t be stupid around visibly malformed lithium batteries.