Looks like Z-Library continues to be the winning option.
Considering Amazon is an American company, as a Canadian I currently have no qualms ignoring IP or rights holdings of an organization that supports a fascist takeover of my country.
So I sent this to my parents, as they've spent hundreds, if not thousands on their Kindle books.
They don't really care. Zero interest in DRM-free backups that I can make them. They don't think it's an issue. They trust Amazon to not mess with their books, and that they'll always have access to wifi and kindles.
Check their libraries for their favourite authors. Get them a Kobo. Load it up with their favourite author's bodies of work before giving it to them. Problem solved.
Disclaimer: I am not responsible for your parents hassling you for more books