I’m primarily a fell runner (and sea kayaker) but I do an occasional triathlon for fun and don’t take it too seriously. I find the shift in emphasis keeps my training fresh and provides some good active recovery. As suggested above I’ll combine runs with a bike ride to my starting point or ride to a loch or the sea to swim.
I’m happy to admit I’m not troubling the leaders in any of my activities but if your primary aims are personal enjoyment and satisfaction (while performing to a standard that is acceptable if perhaps challenging to you personally) then just enjoy whatever you want to do.