As the done/submit/complete survey button takes precedence on the last
page, the save and continue later option will never be displayed on the last
page.
If it"s a lengthy survey and you want the save and continue later option
at regular intervals, I would suggest you to add a page break (helpfile-
https://www.questionpro.com/help/page-breaks.html) before the last
couple of questions as the respondent then would be able to save their
progress just before completing the survey.