I mostly agree with @CawlinTeffid here, but there is a little more work to be done for the operating and file system when needing to look through massive folders. But for most cases it’s not something you’ll as the end user will notice.
Like on Mac if the number of files in a directory is low, it’ll only need to check one inode. When it passes the first number threshold it needs to do a dual lookup, and the more files the more lookups. (This is heavily simplified! It uses btrees to store this information) But the actual maximum numbers of files in any given folder on Mac with hfs+ is around 2.1 billion files. I wouldn’t recommend that, though.