Magento version upgrade can be completed with little to no store downtime if it is planned carefully. The safest method is to create a separate staging setup, perform the upgrade there, and test every feature before switching it to live. This allows customers to keep shopping without interruptions while the work is done in the background. When everything is ready, the final switch only takes a short moment. With the right technical team and proper testing, the upgrade can be smooth and barely noticeable to users.
