You used to be able to, but they removed the ability in late 2015 and they never put it back. I don’t know why.
So now you have two options. Either a routine, as you mentioned, or set up a virtual switch and have that switch coming on run a routine which changes the mode.
If you set up a room for your mode switches, which many of us have done, it may be faster to get to if that’s the issue.
Alternatively, if you just stick with a routine, you can make the routine into a widget so that also gives you quicker access.
In my personal opinion, none of these is as satisfying as the original method of just being able to change it through the app but there it is. At our house, we use mode switches in a room just so we don’t have to scroll through all the other routines.