How to create a sitemap for Google to re-index 40,000 fake pages?

Thanks a lot for the quick response!

404-page – this is something like this – https://www.google.com/search?newwindow=1&sxsrf=ALeKk01ICZAGzfelh5_oigKYDHC4EHk5ww%3A1605752886833&source=hp&ei=Nti1X4j1MMeU-gTvgJK4AQ&q=site%3Aquartercheapersigns.ca&oq=si&gs_lcp=CgZwc3ktYWIQARgAMgQIIxAnMgQIIxAnMgQIIxAnMggIABDJAxCRAjILCC4QsQMQxwEQowIyCAguELEDEIMBMgIILjICCC4yBQgAELEDMggIABCxAxCDAToFCAAQkQJQgwpYvApgxhtoAHAAeACAAW2IAdUBkgEDMC4ymAEAoAEBqgEHZ3dzLXdpeg&sclient=psy-ab ?

You write “Let Google request them and get a 404” – that is, I need to actively post a sitemap with these pages – for reindexing, and vice versa – not hide them in robots.txt?