Amazed no one has mentioned MyAnonamouse. They have open sign ups pretty regularly, the best private tracker I've ever seen. Great for ebook and audiobooks both.
It's alright for free. The slow downloads are still perfectly usable unless there are server-side issues, and they also provide links to other mirrors (libgen.li, which is still up, Z-lib, and IPFS).
Just needed to remake a Z-lib account recently (without an account you can read but not download I think), and an alias from simplelogin worked. With temp-mail services I wasnt getting the confirmation email. And I ain't gonna use my domain for pirating, sorry :)
The torrents are alive; as long as you can get the torrent links from libgen, you have access to the files. (No need to share whole archives either, you can pick & choose).
The name of the pdf file inside the torrent is its md5 hashsum without the .pdf extension.
On libgen.rs you can see the md5 hashsum on the download page; on libgen.li you need to look at the JSON file provided at the link on the search result , as they don't render it on the ui.
Firstly, I search for the book among Telegram book groups. Then, Google/DDG/Bing/Yandex results for "[title of the book i'm searching] filetype:pdf". If neither yields the book, I turn on my Tor and try to find it inside Imperial Library of Trantor. Worst case scenario, I try to find a working Z-Library HS. But some comments here added to my possibilities, such as Libgen (I knew Libgen from onion, but it's interesting to see it also routeable on surface).