Stillwater (2021) - {tmdb-616651}.mp4
or
Stillwater (2021) - {imdb-tt10696896}.mp4
When using subfolders, use the same name for the folder (minus the .mp4 file name extension, of course).
Make sure that in the properties of your movies library, you don’t have a check mark in “Prefer local metadata”.
Otherwise the scanner can be thrown off by embedded meta tags in those mp4 files. (which are incorrect in very many cases)
If you have already added a file into a Plex library and it is incorrectly matched, you may have to perform the Plex Dance to delete this incorrect match. Simply renaming the video file won’t be enough.