About the warmth: If I understand the L5’s design correctly, the frame is acting as a heat sink for the device internals, so that’s why it feels warmer in your hand than most phones. The heat is being actively channeled to the outside.
It will feel warmest while it is being charged. You can see thermal readings in the
Usage application. These readings will vary from low-20 degrees C to, say mid-40s, depending on the activity level. You might see an occasional reading of 85 degrees C (!) for “bq25890-charger,” but that is apparently just a bug in the reading, so don’t be alarmed. (It might be corrected by now…I’m not sure.)
About the display: Note also that if your hand floats over the proximity sensor above the top of the screen (just to the right of the speaker), this will cause the screen to darken until you move your hand away. Hopefully, this will be modified at some point to only activate during phone calls. [Edit: This is apparently fixed in byzantium, so disregard. Earlier L5s were shipped with amber repo installed.]
Here are some tips that have been collected so far: https://source.puri.sm/Librem5/community-wiki/-/wikis/Tips-&-Tricks