It has gotten hot around here but it seems that heat acclimation is no longer being provided.
Last summer I had no problem with it. This year after my first ride in heat (avg temp was 30 degrees) I realized that something was wrong with it. I use an 530 for recording rides, but I am almost fully sure that it works like 830.
More details in a Fenix 6 thread: https://forums.garmin.com/outdoor-recreation/outdoor-recreation/f/fenix-6-series/230759/heat-acclimation-for-fenix-6-and-edge-830/1634878#1634878
As you can see I checked what I could and my last post there confirms that I rode in a heat (see Weather widget data) and the weather station also thought it was hot enough.
Since then I found out there is another place to check weather data related to Heat Acclimation.
I also checked the weather info in GC, placed on the map (top-right) and it shows 31.1 degrees for the yesterday ride.
My 530 shows 1% Heat Acclimation under the Training Status page in My Stats.