Maybe

You'd need to export the Citrine database regularly as Citrine does not use persistent storage

And back the database up somewhere

And those notes would only be available on your device

Running your own relay is another option

It would be less manual than Citrine after the initial setup

And your notes would be available everywhere

In a way it's the most censorship resistant option

If you add your own relay to your list of inbox relays (NIP-65) it will receive and store any events you're tagged in (replies, DMs, mentions, likes, zaps etc) provided that the other user's client implements NIP-65 which most do

Possibly StartOS on a VPS would be the most straightforward option for creating and managing a nostr relay

This is all assuming that nostr relays can be configured to *not* honor delete requests, I haven't checked

Just for storing your own events permanently https://cellar.nostr.wine/ is a good option

As Tony noted though, you won't be able to view deleted notes in clients that honor delete requests regardless

So there's a client issue and a relay issue