A website or an app where you give examples of certain music (type in song name(s), artist(s), link playlists, etc.) and it gives you a list of movies that used that particular music in their soundtracks or suggests you movies with similar soundtracks.
There are sites that let you discover music through movies, e.g.: 1,2 (they display you the content of a soundtrack of a particular movie), but there are no sites (as far as I know) dedicated exclusively to let you discover movies through music. The second site I linked allows you to find artists whose music was used in certain movies, but not individual songs. If you want to find in which movies a particular song was used you have to go to IMDb and use the advanced search function as described here, although, from experience, that search function is not convenient. In any case, none of those websites have a function to recommend movies that have soundtracks similar to the examples of music that you give.
Music defines the mood of the movie, so if you know a song/artist/playlist that resonates with you at the moment, with the help of this platform you could find movies that would most likely also resonate with you.
Recommendation algorithms of various music streaming platforms suggest new music according to your listening history, music that is somewhat similar to what you've listened to before. Combine this with a database of movies and songs used in their soundtracks (IMDb database will work) and you get the result.
You go to the website and type in the search box the name of the song, author, album, or musical genre. You can then choose whether you want to find movies that contain a particular song or songs of a particular artist in their soundtrack or whether you want the platform to recommend you movies with soundtracks that have musical similarities with the example(s) you gave. You can also link playlists from music streaming platforms for the algorithm to have a wider understanding of what type of music you have in mind. It then gives you a list of movies according to your search input.