We upgraded all 19 servers a couple of months back and the process was quite straightforward. There are a few settings you will need to adapt, some others have been made obsolete, but the format of the files and the existing tasks and QMC setup persisted without any hassle.
Make sure you back up all config files and follow the steps.
-This document from Qlik Support "QlikView 11.20 End of Life Upgrade: Known Issues and changes in product behaviour" https://qliksupport.force.com/articles/000047422. If you cannot access the support portal contact Qlik Support for a copy of the doc.
The same day. The development is mainly done in development servers, meaning developers connect to those servers, they do whatever, so after all, is just a few QlikView Desktop upgrades.
We can also have a copy of QlikView Desktop in our laptops, but since we don't have admin access to install anything, we requested IT to create a package users could request and install via group policy: