To be clear, the note will only get deleted on the relays that support NIP-09 right? So if even one relay I connect to doesn’t support it, the note will remain on that relay yes?
You can delete any Nostr note, if the relays you connect to have support for NIP-09. Most common relay implementations such as strfry, nostream and nostr-rs-relay support it.
Here's a nice tool for issuing delete events to your relays: https://delete.nostr.com
Discussion
That's right. It's rare though for a relay not to support it. Also, there can be modified versions of a relay that disable NIP09