➜  ~ bash --version
GNU bash, version 5.2.37(1)-release (aarch64-apple-darwin23.4.0)
Copyright (C) 2022 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

➜  ~ bash -c 'echo ${#PATH}'
578

I'm going to try and develop a bit more information, but I believe the order of execution is:
.zprofile
.zshrc
.zshenv

In my current setup, the rbenv init is running (correctly) in my .zshrc.
But, I add a couple items to the path in .zshrc and several in .zshenv (including the Apple cruft)
The result is that although I correctly eval'd the init during my .zshrc; I can't run /opt/homebrew/Cellar/rbenv/1.3.0/libexec/rbenv init - zsh
once the shell is initialized.

Let me see if I can determine the precise path length that causes the wheels to fall off the cart

Originally posted by @BiggerNoise in rbenv/rbenv#1593 (comment)