I just saw in the latest beta of the FR245 that the perception is one of the new feature (https://forums.garmin.com/sports-fitness/running-multisport/f/forerunner-245-series/261604/forerunner-245-series---beta-software-version-6-85-now-available):
Added the ability to rate the perceived effort and feel of a Run, Bike, or Swim activity. The prompts appear during activity save. Go to [Activity] Settings > Self Evaluation for options.
Does anybody knows if the SDK permits to read it or set it at the end of a session?