I am very unhappy with this change. I always liked that I could keep my ebooks/Polar Libary in my Nextcloud, but now it sounds like that isn't possible anymore

I am very unhappy with this change. I always liked that I could keep my ebooks/Polar Libary in my Nextcloud, but now it sounds like that isn't possible anymore :-/ I tried the cloud version in the past, but it had only disadvantages for me.