1
In file explorer find the folder you wish to stop syncing and right click on the folder.
2
In the menu find OneDrive and select "Stop Sync"
3
If that was the only folder you are syncing you will no longer see it in file explorer. If you are syncing other folders as well then you will still see it and will need to delete it. You can verify that it isn't syncing anymore by selecting the folder and looking at the "Status" column. If it is blank than you have successfully stopped syncing that folder.
4
To delete the folder, right click it and select "Delete" or the trashcan icon.
The folder will now stop syncing and be removed from file explorer