I found a thread on the forum (URL copied below) which was asking exactly what I am looking for. However, it is 4 years old and this page also has many ideas suggested but they haven't been addressed. Thus, I am not sure if my idea will be addressed but I will mention it anyway.
https://support.box.com/hc/en-us/community/posts/360052391193-How-To-ignore-Files

There are certain files I want Box sync to ignore or block. I would suggested allowing the user to create a configuration file in the root folder for the same in which we can specify files to ignore or block. This way, Box sync can read this file before a sync and honor it.