I can't answer any arbitrary scenarios. All I can do is recommend the official procedure: What to do before you sell, give away, trade in, or recycle your Mac - Apple Support
When you do that, the hard drive will still have all of your encrypted data on it. But the data is encrypted, and at a very low-level. To anyone looking at the drive, at any level of detail, they will see only random data if they don't have the password.
If you wanted to, you could still write random data, or all zeros, 1's, whatever, over the entire disk. But you would have to start with the official procedure. Then write your data. Then repeat the official procedure. But that really isn't going to increase your security any way. Encrypted data without a password is the same as random data.
Apple did remove the option to write zeros, 1s, whatever to the drive, but that was only for social media and marketing concerns in our post-truth world. The process still works. You can still do it. But because of the way SSDs work internally, there would still be small bits of data that would not be overwritten. It is extremely unlikely for anyone to ever extract anything from those dark, low-level recesses of data. But that extremely low risk is enough to drive a good amount of social media click-throughs. So Apple got rid of it. And then later, Apple took the extra step to make sure that all data is encrypted before being written no matter what. When running a company at Apple's scale, it is a non-trivial task to manage internet lies.