SQL Server Always On - security updates without DB disconnecting from application

Our real-time communication application relies on database access, and it cannot be disconnected from the DB when running. Recently our customer’s DB maintenance team notified us that the DB will be occasionally disconnected from the app, possibly also during application working hours - due to security upgrade reasons. The blackout gap can be c.a. 2-minute. The question is: Is it possible with SQL Server Always On setup (this is what they have) to maintain **uninterrupted** DB access (from application perspective) during upgrading nodes of the SQL cluster ? Our understanding is that SQL Server **Always On** setup (as the name indicates) should be always available, regardless of a single node failure, or in case of intentionally executed upgrade on subsequent individual nodes (even if taking these offline, if required). We believe this should be possible with some kind of setup. Or alternatively does the “Always” mean “**almost** always” (with e.g. 2 minute time required to fail over to some standby instance, etc..) ? Can anyone confirm possibility to update software of **individual nodes** of the cluster (Windows Updates + SQL Server engine updates) one-by-one, eventually upgrading all nodes – with maintaining uninterrupted database access by the application during this process ? Could anyone share a link to documentation or article describing how to configure this capability? (We plan to share these links with the DB maintenance team).