How to find all of the pages in the web

We are in the process of migrating from one domain to another. Most of the pages were identified using Screaming Frog, which looks normal. However, the client provided an additional list of URLs used for Google Ads, and it seems these URLs were not detected by Screaming Frog. What could be the reason for this? It is important to note that these pages were not included in the sitemap and did not have any internal links leading to them. Are these type of URLs could be called orphan pages? Is there a way to identify these URLs without provided help from client side?

Maybe through competitive analysis tools. Lookup their domain. You can also look in Google's transparency center to find ads running on their domain.
While your at it, might as well give FB's ad library a visit, too.

https://adstransparency.google.com/https://www.facebook.com/ads/library/

try get help from tools, you can find about it.