On Ubuntu 20.04, I installed auctex, eglot, company, yasnippet into
Emacs through straight as shown below:

```emacs-lisp
(straight-use-package
 `( auctex :type git :host nil :repo
"https://git.savannah.gnu.org/git/auctex.git"
    :pre-build ,(pcase system-type
                (`berkeley-unix '("gmake"))
                (_ '(
                    ;("bash" "-c" "cd ~/.emacs.d/straight/repos/auctex")
                    ("./autogen.sh")
                    ("./configure" "--without-texmf-dir" "--with-lispdir=.")
                    ("make")
                    )))))
     (setq TeX-data-directory (straight--repos-dir "auctex")
           TeX-lisp-directory TeX-data-directory)

     (eval-after-load 'info
        '(add-to-list 'Info-additional-directory-list
                      (concat (straight--repos-dir "auctex") "doc")))

(load "auctex.el" nil t t)
(load "preview-latex.el" nil t t)
(setq TeX-auto-save t)
(setq TeX-parse-self t)
(setq-default TeX-master nil)

(use-package company)
(add-hook 'after-init-hook 'global-company-mode)

(use-package yasnippet)
(require 'yasnippet)
(yas-reload-all)
(add-hook 'prog-mode-hook #'yas-minor-mode)

(use-package eglot)

(with-eval-after-load 'tex
  (define-key TeX-mode-map [remap TeX-complete-symbol] #'completion-at-point))
```

Then I open the following tex document in Emacs

```
\documentclass{paper}
\usepackage{braket}
\begin{document}
   Some testing comes here.
\end{document}
```

and enable Eglot (M-x eglot), but I find that Eglot Failed to do the
completion for commands defined in specified loaded packages for
auctex. But TeXstudio doesn't have this problem.

See the screenshots in attachments for more detailed info.

Regards,
-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
NO. 552 North Gangtie Road, Xingtai, China