Documentation suggests manual offline install of updates is only possible with Netinstall. Is it not possible to update using WinBox with packages downloaded to PC by uploading them to “Files” on router that is offline?
If there is something in MikroTik documentation, which suggest that, please share a link with us so we can take a look, but yes, it is possible to upgrade or downgrade RouterOS without help of Netinstall.
https://help.mikrotik.com/docs/spaces/ROS/pages/328142/Upgrading+and+installation#Upgradingandinstallation-Manualupgrade