I have a Win UI 3 app that checks it here is a new update available, it dowloads the installer, but is it possible to execute such installer without closing the app?
Is it to complex? or should I just have the user do it manually?
NO. The executable is in memory (and may have locked files or resources). In order to get an update it will have to be relaunched. If your code is modular, think plugins, these could be updated in place.