Currently are aware of Lookout 6.7.1 (the last version pushed) running Citadel (SQLServer 10.5.2500) on some of our Win10pro 64x machines. It works great. We have also tested install on Windows 11 and this works great as well.
On some test machines we have many versions of SQLServer installed including v16(newest) along side v10 and everything still works. I have not tried, but it may be possible to backup and restore the database to newer version of SQL and edit the connection string from the System settings menu.
Work is being done to transition out of this, but as significant development has been done over many years and many important client systems still running, we will continue to find ways to make it work for now.