OK if this is on a domain then do the net use command i gave you - if that works as administrator from the command line all good.
Then once you have done that do the same command again but substitute the c$ with the actual name of the share that you have create and see if that also connects with a new drive letter and confirm you can read and write to it
Once that is done you need to delete those map drives (this is important) net use (drive letter) /d - so for example
Net use t: /d
and then try and do the same commands to access the share agan but substitute the username that is being used to start node red (how are you starting Node-red - pm2 ?? or some other manager ?)
If all of that works and you can read and write to the drive, you then need to delete the drive letter again and once again do the net use command to access this drive - but this time on the end enter
/persistent:yes - which will surive reboots
Then try it via node-red