Most if not all journals in my field allow you to upload the final accepted PDF that you have typeset in latex yourself to arxiv. We even put "accepted in $journal" and the DOI in the comment field. This includes all the changes you have made in response to referee comments. What you can not upload is the finial language-edited and nicely layouted version that the journal has build from your submission.

arXiv is not only for pre-printed. Whatever paper you legally put on your website can and should go there (or Zenodo, Figshare, OSF, etc).