So, I used to use Evernote to store my PDFs. But a lot of the PDFs I was buying were from massive adventure and setting books that exceeded the per-file quota. So I started putting them into Google Drive. Then I got tired of managing PDFs in multiple locations, so I migrated everything to Google Drive. I was running out of space of on Google Drive, so I bought more capacity. I'm worried about having all my eggs in one basket and am kinda OCD about backup, so I back up to a separate cloud archive solution. I want some things instantly available, so I'm constantly fiddling with which folders to have synced from Google Drive to my local computer. I have the Drive Thru RPG app installed and synch all my DTRPG content to local storage.
I have a lot of homebrew, licensed, and purchased content on Foundry, hosted in The Forge. I also have the software installed on one of my computers so that I can use The Forge module to backup all my content locally (on top of the snapshots and backups in the cloud through The Forge). That also get cold archived to separate cloud storage.
I spend more time organizing my digital content than I have ever spent organizing bookshelves.
People who work in information governance should not buy digital TTRPG content. ;-)