Using (use-package ...) with Emacs 29+

Question

I am using Emacs 29.1, which ships with use-package, and I want to install and load the MELPA bm package through the init file.

I am using the following test-init.el init file:

(defun my-packages ()
  (require 'package)
  (add-to-list 'package-archives '("gnu"   . "https://elpa.gnu.org/packages/"))
  (add-to-list 'package-archives '("melpa" . "https://melpa.org/packages/"))
  (package-initialize)
  (require 'use-package)
  (setq use-package-always-ensure t)
  (use-package bm))

(my-packages)

and I start Emacs (using the new --init-directory switch) with:

/usr/bin/rm -r /tmp/emadir/*; emacs --init-directory /tmp/emadir -q --load /tmp/test-init.el

That is supposed to start Emacs with test-init.el and using /tmp/emadir as init directory, after emptying it. Emacs gives the following error:

⛔ Error (use-package): Cannot load bm

A possible workaround is to move the (use-package ...) expression at top level, that is:

(defun my-packages ()
  (require 'package)
  (add-to-list 'package-archives '("gnu"   . "https://elpa.gnu.org/packages/"))
  (add-to-list 'package-archives '("melpa" . "https://melpa.org/packages/"))
  (package-initialize)
  (require 'use-package)
  (setq use-package-always-ensure t))

(my-packages)
(use-package bm)

That gives no errors, however, this is inconvenient for me, as my real init file is huge and I need to use functions to organise it.
What can I do to nest (use-package ...) calls inside functions?