Go by feel unless you’ve got some racing goals. If you’re just trying to get fit the you can sub/mimic/shuffle your training plan around the best sunniest weeks and get the tan lines going while you can. Generally speaking though, there’s a high possibility of failing workouts if you’re not fresh enough because the outdoor stuff added too much TSS or muscle fatigue that you’re not used to.
If you’re happy indoors on the trainer, don’t feel like you have to go outside for a ride in the sun or something. Loads of people now get just as much buzz out of an indoor training session as they would from riding the same little route outside. The traffic, extra preparation and time needed often sullies the enjoyment of an outdoor ride for people too so it’s not surprising you see people doing indoor sessions on beautiful days on Strava feeds.
Personally, if I’ve been riding indoors a lot, I get a craving to ride outdoors, and vice-versa. I’ve only just managed to sort out a way to train indoors last weekend and all my rides this year have been outdoors and random. I couldn’t care less how sunny it gets now, I just want to do some indoor structured work and see how I handle ERG intervals! That’s my current idea of a good time