This picture should give you an idea of how secure it is. However, there are other things to consider. Some people like to separate their seed words and store them in different locations. A 24 word seed can be split 3 ways (8 words each). This can lower risk of physical theft of your funds because your seed isn’t all in one place. The downside is that it’s more complex to store. People usually have their wallet and a backup seed. But if you split up your seed into 3, then you also should have an extra backup as well in case one of those 8 words is lost or stolen. So now you have 6 locations holding your backups.

And there are some who think that some form of quantum computing could access bitcoin wallets and that they’ll target 12 seed wallets first. Idk how much I buy into that though. The other thing is that memorizing your seed is also risky. You might think you have it memorized but you could easily forget it over time. So you most likely have to find your backup when you need to access your wallet. So having 12 words on that backup instead of 24 isn’t giving much additional convenience.