Due to security vulnerabilities, struts2 needs to be upgraded to latest versions i.e vulnerable free (2.3.32 or 22.214.171.124) which is vulnerabilities free.
After upgrading s:submit action button will not work because it is disabled by default due to security vulnerabilities.
<s:submit align="center" action='Login_loginUser' value="Login"/>
So that to make it as working, we need to add the following constant parameter in struts.xml
<constant name="struts.mapper.action.prefix.enabled" value="true"/>
Then build the application and redeploy the application and check. We will assist you, if you need any help.