Immich can search by star rating, but you need to enable the feature as it's not enabled by default. Go to Account Settings / Features / Star Rating.
After that, it appears in your search options/filters

A place to share alternatives to popular online services that can be self-hosted without giving up privacy or locking you into a service you don't control.
Rules:
Be civil: we're here to support and learn from one another. Insults won't be tolerated. Flame wars are frowned upon.
No spam posting.
Posts have to be centered around self-hosting. There are other communities for discussing hardware or home computing. If it's not obvious why your post topic revolves around selfhosting, please include details to make it clear.
Don't duplicate the full text of your blog or github here. Just post the link for folks to click.
Submission headline should match the article title (don’t cherry-pick information from the title to fit your agenda).
No trolling.
No low-effort posts. This is subjective and will largely be determined by the community member reports.
Resources:
Any issues on the community? Report it using the report flag.
Questions? DM the mods!
Immich can search by star rating, but you need to enable the feature as it's not enabled by default. Go to Account Settings / Features / Star Rating.
After that, it appears in your search options/filters

Seems you can search by rating in immich: https://github.com/immich-app/immich/discussions/11777
Though you can't use greater than, less than, etc., or sort by rating.
If you're willing to use something designed for porn, you can use stash: https://github.com/stashapp/stash It can definitely do those, though I'm not sure if it imports existing metadata. You can probably script that. It doesn't scream "this is for porn" in its interface, either, you might not even notice in brief use. The most sexual thing in its interface is two metadata labels it has, "last O at" and "O count".
I'm aware of Stash. I wouldn't have thought of it and that might actually be a good solution. I'll spin up a copy and see if it'll work. Thanks for the suggestion. :)