Stay safe: keep your server up-to-date!
Minor Nextcloud releases are security and functionality bug fixes, not rewrites of major systems that risk user data! We also do extensive testing, both in our code base and by upgrading a series of real-world systems to the test versions. This ensures that upgrades to minor releases are generally painless and reliable. As the updates not only fix feature issues but also security problems, it is a bad idea to not upgrade!
This is, of course, also true for apps: Keeping them updated has security benefits, besides the new features and other bug fixes.
If you are maintaining a mission-critical Nextcloud system for your enterprise, it is highly recommended that you get yourself some insurance (and job security… who gets blamed if the file handling system isn’t working as expected?). A hotline to the core Nextcloud developersu is the best guarantee for reliable service for your users, and the job safety of you as a system administrator.