Hello,
For CI testing of my emacs-based projects, I customize package-user-dir in an emacs -Q session to install the required packages in a "sandbox" area.
As an example, for my eless project, I run "make vcheck"[1] to install the latest Org stable version in an area separate from the user's default ~/.emacs.d/elpa by customizing package-user-dir in a test setup file[2].
The problem is that that approach does not work on emacs 27.x, as it probably depends on early-init.el even in emacs -Q sessions.