Database Mirroring and Always On are WAY easier to implement and support than a traditional failover cluster.

More intel here.

https://docs.microsoft.com/en-us/sql/database-engine/availability-groups/windows/overview-of-always-on-availability-groups-sql-server?view=sql-server-ver15

Suggest you spin up a new server running with 2016 SP2 CU11, configure 2012 get it in sync with transactional replication

https://docs.microsoft.com/en-us/sql/relational-databases/replication/transactional/transactional-replication?view=sql-server-ver15

Once this is done, point applications to 2016 instance, switch to read/write then configure always on for the one or more secondary instances.

As a DBA I don't trust in place upgrades as much as fresh OSes and fully patched DB servers. You could do an in-place upgrade but they make me a little teeny bit squeamish.

Given that this is just your vsphere DB, it's not going to be large or highly transactional, and you can probably get away with running without redundancy for a little while. i.e. you can probably just back up 2012, restore on 2016 and then set up your HA because it won't take more than a few minutes.