The issue isn't the user-hosted content - I'm running a release build of Immich on my own server and Google flagged my entire domain.

Is it on your own domain?

Yes, my own domain.

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Is the subdomain named immich or something more general?

The subdomain is "immich", which has crossed my mind as a potential flagging characteristic.

Thanks for the datapoint. I agree with sibling that it shouldn't be a problem, but am glad to discover from this thread that it may be.

Don't accept that rhetoric. Google shouldn't get to decide how you can design your own website.