I point to this as the reason (in addition to other points made above which are all likely contributing as well). On the trainer your variability around your target wattage is going to be pretty low, especially in ERG. When you go up a rolling climb, you are engaging different muscles, sometimes standing and taking your power above your NP average for your ride. Going down the other side you may coast or soft pedal but you probably generate less watts going down than going up.
So your ride ends up being a rolling over and under interval with higher peaks and lower lows than you would ride on the trainer. That spread between the highs and lows is what’s killing your NP.
I have been doing 3 hour group rides on Saturdays and the same loop on Sunday solo pretty frequently. What I have found is that I am a guy that likes to keep my average power high. I ride pretty steady and consistently hard but I don’t mash up hills when I do my solo version.
So I can feel more thrashed while having a lower average power on Saturday because it’s a “fly up the hills” and coast down/recover kind of ride. When I go solo I see higher average power but feel a lot more fresh at the end because I aim to keep it steady and end up with a much faster average speed as well.
TLDR: I think the hills, wind and roads are pushing you above your tempo/sweet spot pace and that’s causing you to need more rest. That variability is hurting your NP whereas I bet on the trainer your NP and AP are pretty close if not spot on for your intervals.
You can go into the career page on TR and search through some of your rides. I did a search in my “recovery” ride where I did what I thought was just a few sections of hardish pedaling. For fun I searched to see where I held over my threshold of 332 for at least 30 seconds. It turns out in a 63 minute recovery ride I rode over threshold for 30 seconds straight (30 seconds or more) 10 times! If I were doing a recovery ride on TR or even a sweet spot session, I can tell you the number of times I would go over threshold for 30 seconds would be 000*0=0.
That variability adds up and it will definitely impact your ability to produce consistently high wattage. Next time you go out, try to stay under your FTP on the hills, in the wind and on the bad road sections and when the road is easy try to bring your wattage up to 250 for those sections. I bet if you shoot for a narrow 25 watt band your NP will be a lot higher on the next ride.