Spicy pillows are basically caused by 1 of 2 things:

1. Heat

2. Being fully charged all the time

Recording video consumes a considerable amount of power, leading to heat. The display less so, unless you're operating at maximum brightness all the time.

#2 is what killed my Pixel 3 after only about 2 years. Once I started working from home, I had a bad habit of letting my phone sit on the charger all day and after about 3 months of WFH the pillow got spicy.

For a phone that's going to be repurposed as a server, I wonder if it'd be worthwhile to open the case and attach a heat sink to the battery.