Google not crawling my site anymore

My site has been continuously losing indexed pages in the past couple months, and I know this has been an issue for many people. Every day more of my previously indexed pages are listed as "Crawled - Not Indexed". But when I go into the Crawling Stats in my GSC and look at the most recent requests, I see that a page has been crawled a couple days ago. But when I look that page up in GSC it is telling me that it hasn't been crawled since September! Also, my site had some server issue for one day in October and google tried to index some pages that day and got a 500 response. I tried to re-validate those pages (20,000 pages) and after over a month, the verification failed and I can see that in this month it attempted to validate 6 of those 20,000 pages - and I know for a fact that all of those pages were not throwing server errors in this period. When I check my crawling statistics I can also see no server errors ocurring since. I've also added a new page to my site two weeks ago and manually requested it to be crawled. When I check the URL it still tells me that google doesn't know about this page. The page is added to my site's header bar and is thus linked to on every single page. It seems like my website is basically not being crawled at all anymore ...