I have to say, that I’ve suffered from exactly the same (struggle … motivation e.t.c) and putting a power meter on my outside bike has transformed my riding and enjoyment of the sport, most outside rides are now zone 2, and it takes away the “it was only x mph, I’m rubbish, why do I bother”, as I’m not trying to beat my time on a route … I’ve been doing different routes, which have been getting longer … so my endurance improving
I do try to stay consistent on the zone 2, so a little harder on the downhills, and softer on the uphills,