So first off - that link doesnt actually give you a solution to what you want to do. They awnser in the link is what the run from here option can do. For the run from here to work as it says in that topic it needs
This is activated and shown to the user by the following
Now a browser where you have completed the steps before manually will not have chrome driver active and therefore the script wont run. However like the guy in the other topic has said, if you run a script and keep that browser open, the following steps you have will be able to run with the run from here option. (although from reading above, this is not what you want to be doing, and frankly this will cause you alot of issues)
Now to go back to your first point -
Now i havent personally done any mobile automation testing but there is the option to do so. I cant see why what you are trying to do shouldnt work with the mobile testing however like i said, i havent done any mobile testing before with katalon. I will link a few docs that might be worth a read. If it doesnt make sense, hopefully someone with more experience in the mobile aspect can help you.
That being said, you could create two seperate test cases - one for the mobile steps which then gets called in your main test after you “activate your login page in the browser”
https://docs.katalon.com/katalon-studio/docs/mobile-switch-to-native.html#description-
https://docs.katalon.com/katalon-studio/tutorials/setting_mobile_application_automation.html#installing-nodejs
https://docs.katalon.com/katalon-studio/docs/mobile-on-windows.html#verifiying-the-setup
Hope this makes sense 