I do not want to give any custom solution here since it looks like that this feature is already given by a third party plugin.
You should try this plugin: https://extensions.joomla.org/extension/system-redirect-on-backend-login/
According to the few lines of documentation of the plugin it does exactly what you need. Even more, since you can set specific user group to be redirected to a component (set by you) after admin login. I did not try that but it looks like it is a newer plugin, actually 5 months old at the moment. And I just downloaded it to looking into it - it is free - and it is a nice, simple system plugin with actually 15 lines of code which checks the user and the usergroup and if the user group is set by you to redirect then it calls the Router to redirect to the given component.
The plugin code could be a bit improved, cleaned here and there, as I see it was made in a hurry by a PHP programmer who has about a strong medium level understanding of Joomla back-end programming (which is a good level considering the complexity of Joomla today). It is quite useful and looks like a working code base for this admin redirect. Nice and neat solution for this simple job. You can later improve this plugin for yourself a bit if you would like to...