Is there a music score search engine?

There is a music score search app based on ngrams called Peachnote. The idea is to enter a melody intervalically, and the app searches a database of scores pulled from IMSLP and other sources.

Here's an article extolling Peachnote's virtues. (Adrian Giordani. 27 May 2018. "Who or what really inspired the Viennese wunderkind?". Accessed 27 July 2020.)

And here's the original paper about Peachnote. (Vladimir Viro. 2011. "Peachnote: Music Score Search and Analysis Platform." Accessed 27 July 2020.)

There is also, an app for Android (link is http, not https), but I don't have an Android, so can't confirm.

Now the bad news: I couldn't get the Peachnote website to find famous classical pieces that I know are on IMSLP. Could be user error, could be many things; I wish you better luck.

Another question in site gave me an answer. It is not quite like the book that I mentioned in the comments. You don't need to identify the intervals between the notes (as the book required) but only whether the notes go up, down, or stay the same. So, I expect that you need a longer sequence in general but it works surprisingly well with even a short sequence. I just tested it with the first theme from the second movement of Beethoven's fifth symphony. I entered: *UURDDUD. The * represents the first note so I said that it went up twice, then repeated a note, down twice etc. The theme that I wanted was not the first hit but it was on the first page. Slightly confusingly, a later instance in the same movement that did not continue as I expected appeared first. To be sure that you have the right hit, you will need some ability to read music.

I am talking about the Contour Search in this site but the other functions may be useful as well.

https://www.musipedia.org/

I expect to become a frequent visitor.