The best of the suggestions in the Twitter thread brings us to the Arduino Entropy Library, which uses jitter in the microcontroller clock to generate truly random numbers that can be used as seeds.

The exact placement of clock edges will vary both within a clock period and from one clock period to the next. This variance in period is known as jitter. This article explains a some of the key ...

This white paper explains how jitter changes the period of a clock and how to ensure that jitter has correctly been accounted for in the calculations for timing closure. Period jitter is the deviation ...