I know that I can bypass the warning, but the photo album I sent to my mother-in-law is now effectively inaccessible.
It may well be a false positive of Google's heuristics but home server security can be challenging - I would look at ruling out the possibility of it being real first.
It certainly sounds like a separate root issue to this article, even if the end result looks the same.
That area will show you the exact URLs that got you put on the block list. You can request a review from there. They'll send you an email after they review the block.
Hopefully that'll save you from trying to hunt down non-existent malware on a half dozen self-hosted services like I ended up doing.
I guess a workaround Google's crap would be to put an htpasswd/basic auth in front of Immich, blocking Google to get to the content and flagging it.
Btw, folks in the Jellyfin thread tried blocking specifically Google bot / IP ranges (ASNs?) https://github.com/jellyfin/jellyfin-web/issues/4076#issueco... with varying success.
And go through your domain registration/re-review in G Search Console of course.
Thus if I started hosting my Immich instance, I would probably put it behind "pxl.domain.tld" or something like that.
Not a garantee to pass the Google purity test, but, according to some reports, it would avoid raising some redflags.