Difficulty Keeping All Pages Indexed

ecommerce site with around 2500 Product pages as well as 100+ Collection pages. I often find dozens of pages that are not indexed. it is a lot of work getting them back on Google Search I am pretty diligent about checking GSC and finding pages in Crawled - currently not indexed or Discovered - currently not indexed, etc. I can almost always Request Indexing and get them indexed. Then for some time it is fine, then months later a new group of pages show up on the lists. I do try to make the descriptions a bit more unique than competitors as I understand if they skip over duplicate content. Also try and fix anything else that might be wrong. Is there anything i can do to keep the entire site indexed?