The problems with trainers go beyond heating. Trainers typically don’t have any movement side to side as experienced outdoors, so you’re unable to engage certain muscles because the bike is more or less locked in place. My one friend was able to bridge the gap a bit with a rocker plate but still can’t replicate outdoor power indoors, I use the same bike on and off the trainer and my outdoor efforts are more powerful or done at a lower HR, typically both
Intervals.icu actually let’s you specify an indoor and outdoor FTP, and we have threads here asking for that functionality through TR on a regular basis