With a fair degree of experience the RPE calculator for running workouts in TR tends to under estimate especially for longer runs. As a way to get an estimate, I use a free Training Peaks account and then have Garmin Connect sync out to that. If you use a heart rate monitor (or without) it will give you a TSS value. Usually I just put that into the calendar in TR so I have total weekly TSS.
It’s still an estimate so I have no idea if the value is real or not but it seems about right most of the time.