Setup new Window Server Failover SQL Cluster using an existing database I see lots of resource but all of them are instructions on how to setup SQL fail over cluster (not availability group) from scratch using empty database instance.

I have a single non cluster database running now and I would like to convert it into HA fail over by adding another node/vm.   I'm not 100% sure but some Googled resources say you cannot convert a non-clustered SQL Server instance into a clustered instance.

What would be the best method or approach in my case to go about converting my existing Database Instance into HA using FCI (not Availability Group) ?
Build a new cluster with an FCI and migrate the database using backup/restore.  If you are not using VMs and need to reuse the existing server, then create a new 1-node cluster with an FCI, migrate the database, then rebuild the existing server, add it to the cluster and expand the FCI onto the second node.