You had a lot of questions, all of which led to the same answer. APFS uses encryption by default. Installing macOS High Sierra on a Mac with all-flash storage (in other words, not a hard disk, not a Fusion Drive, but all flash and nothing else) then there is no need to do anything else. macOS already performs all of the housekeeping minutia necessary for using flash storage to its maximum performance and lifespan. Security is a fundamental component of it.
Does TRIM or garbage controller exist on these macs?
Yes, it has to, and there is nothing you can do about it anyway.
Does file vault 2 encrypt deleted data?
It encrypts the entire storage device. Trash, deleted Trash, all of it. It's encrypted from cradle to grave and everything in between... the only correct way to handle secure data.
When do secure files become secure anyway? The moment you decide to throw it away? An hour before? A minute after? Last Wednesday? When exactly? The answer should be obvious. Before you "secure" them, many non-"secure" files and copies of files are created in the normal course of working with them. What's worse is that multiple redundant copies are normally stored in sectors of a hard disk totally inaccessible to the operating system. If they weren't secure then, they can't be secured now. That's even more the case with flash—because of TRIM.
How does this work now secure erase has been removed.
Taken to its literal extreme, "secure erase" was never capable of doing everything its name implied even with magnetic media. The advent of flash memory (which is all Apple is interested any more) and the manner in which it needs to be used was the final nail in its coffin.
