It will depend on your Windows OS on the existing cluster - you can only go from 2012 to 2016, or 2016 to 2019 - but not from 2012 to 2019 (only one version up). If the goal is to get to 2019 then you would need to add the 2016 node(s) - migrate the cluster to the new nodes, remove SQL from the old nodes and evict them. Then repeat by adding the 2019 nodes.
Once you have the cluster reconfigured - you can then upgrade SQL Server.
With that said, I wouldn't approach it this way - I would create a new cluster with the latest OS and SQL and then migrate. Yes, this does require changing the connection strings, but it is much safer overall. It allows for recovering back to the original system if there are any issues - and there will be issues.