Yes, login script is a possibility. But is it the best practice? I bet there is at least 5 different ways to do this. Which also means that when time has passed, I’ve forgotten where I did this settings, and when there becomes a need to do changes, I’m not going to find out where I put this. In my mind there is a place where network configs belong.
/etc/network/interfaces.d/ would be the place I’d expect to find this sort of config. But this seems not to be the correct location in manjaro.
I’d prefer this to start before login though, and be independent on which user(s) has logged in.