Just curious…how many categories do you have? I suspect you might have lots of categories.
I have dealt with this too. Try this. Go to Data Validation. Next to Criteria you will see “List from a range” and to the right of that you might likely see a range. In the help article you referred to, the range there was B2:B58. Make the 58 a bigger number to give yourself room to add more Categories in the future without having to go through the process you currently do. Making it 68 will give you room to add 10 more categories.
My range shows A2:A339. I have 334 Categories so my number is big. So, I have enough room to add a few more categories before I will need to increase my 339 number.
This should allow you to add your new category where ever you want to which is what you currently like to do.
Do you know you can sort your categories tab. Select the whole tab as your range then go to Data/Sort range. You may find this helps with your organization of the Categories tab.