I installed animate(19.2.1). But when I open it, a window pops up for 1-2 seconds, then closed, why?

Need make sure which ever animate version you had installed before is completely uninstalled and then install the versions you want. 20.0.3 is actually pretty good. They have worked most of the bugs out. 

reset your preferences, http://helpx.adobe.com/flash/kb/re-create-preferences-flash-professional.html

or remove

Win: C:\Users\\AppData\Local\Adobe\Animate CC \ and
C\Users\\AppData\Roaming\Adobe\Animate\\

Mac: /Users//Library/Application Support/Adobe// and
/Users//Library/Preferences/Adobe/Animate//