The higher end Elite trainers use an optical torque sensor to measure power, at least the Drivo and Direto use this system which isn’t subject to temperature fluctuations. It’s one of the reasons I went for the Direto as all my other Power meters suffer to a greater or lesser from heat build up in my shed.
I had a Vortex for a short period but it went back after a few uses as it wasn’t the greatest trainer for many reasons including the one you mention.
https://www.elite-it.com/en/innovations/Optical-Torque-Sensor