Add samba folder to favorite into finder sidebar
I found out, that the following process adds a folder mounted on a samba share to the sidebar/favorites in my finder. They 'survive' a restart of my mac. I guess they also work as intended if you reboot the NAS/server/whatever. To achieve that, do execute the following steps:


Mount the shared folder (it should be listed in the sidebar under 'Shared' within the finder).
Within the finder, go to View -> Show Path Bar
Navigate to the folder within your SMB share so that you are in the folder that you wish to add to the sidebar.
Grab the icon at the bottom above your status bar left of the name of the folder you are in and drag it to your sidebar.
With a click on this sidebar folder you should land/stay in your desired folder on your samba share.
(optional step) Go to View -> 'Hide Path Bar' if you don't like this additional information.