How many bugs you encounter is unfortunately not a good metric, because devs will compensate by just thinking harder. The goal is rather to not need to think as hard, which increases productivity and helps out your team members (including your future self).

It took me a few months of working in an immutable-by-default language before I had the epiphany that everything is exactly like it’s written down in code (so long as it’s not marked as mutable). I don’t need to look at each variable and think about whether it might get changed somewhere down the line. A whole section of my brain just switched off that day.

As the other person said, there’s also nothing stopping you from using mutability, it’s just not the default, because most variables simply don’t get mutated, even in C code.
But I would even go so far that Rust is actually making mutability fashionable again. It has introduced various new concepts in this regard, which you won’t know from other languages.

For example, you can opt a variable into mutability, make your changes and then opt out of it again.
And if a function wants to modify one of its parameters, you have to explicitly pass a mutable reference, which is visible both in the function signature and where you’re calling the function.

But perhaps most importantly, it blocks you from mutating variables that you’ve passed into a different thread (unless you wrap the value in a mutex or similar).
In most of the immutable languages up until this point, the immutability was achieved by always copying memory when you want to change it, which is insanely inefficient. Rust doesn’t need this, by instead requiring that you follow its ownership/borrowing rules.

Edit:
I also don’t know what you heard, but this is for example written in Rust: https://bevyengine.org/examples/3d-rendering/bloom-3d/
The code is right below. It uses lots of mutability…