On the forum, I saw that mixed targets were fixed for Garmin, but I’m not sure whether they’re fixed for Suunto and Coros.
As for Suunto, you can create mixed targets in the Suunto app (I haven’t tried executing it). From what I read, Coros does too.
I am in the process of buying a new watch and want to confirm which brands support this feature before spending money on a new one.