What does new yellow circle arrow on folder in notes mean?

If you shared notes on iCloud then one of the collaborators may have edited your notes and you are yet to see it.

If you open it and review the changes it will go away.

It is similar to blue dots on Unread Messages. It is Yellow in the Notes.

It would be better if you can please re-post with a screenshot, in order to understand the phenomenon better. Images/pictures speak louder than words. 

Please understand this is a public forum: While attaching a Screenshot, do not provide any personal credentials, such as IP address, Card detail, email id, apple id, IMEI number, Serial Number, Phone number, Order ID, if you are sharing a map ensure your location is not identifiable, etc.

With the limited information that you have provided, It is hard to even guess the problems faced by you. 

You may get faster and better responses to your query by --> Writing an effective Apple Support Commun… - Apple ...

Please re-post with detail so that someone else can help.