Dynamic remarketing lists longer than 30 days are not auto generated. As you will likely know if you have setup a dynamic remarketing campaign, 4-5 lists are automatically created.
What is not immediately obvious is, 30 days after someone has left your site, you will no longer be showing remarketing ads to them. Unless you decide to create additional lists with a longer membership duration and apply them to your adgroups.
The example above shows a retail example, where first I have created a basket abandoners list for 540 days (the max duration). The rules involve someone who has visited a page with a page type including “cart” and not reached a URL with “success” included. These details may change for you, but the principles are the same.
The only difference between creating a normal remarketing list and a dynamic remarketing list is: You are using the custom parameters to define the rules. In the second example on the video above, I have specified that the list should be for product pages. This means anyone who has looked at a particular product rather than just the home page (example). That way, Google Ads will show the product to the potential buyer. Be sure to exclude people who have reached success pages if you implement this one.
If you are using dynamic remarketing for other types of businesses and your custom parameters are different. Just look for the other ones and apply the principles in the way I have described above. I have used 540 days, but it is likely that performance will vary based on the amount of time which has gone by since the visit. I also recommend other lists with different timeframes split by adgroup, bidding accordingly.