Google is rolling out a fix for broken Chromecasts
Briefly

Google is resolving issues affecting Chromecast 2nd generation and Chromecast Audio devices, which experienced "untrusted device" errors disabling casting. Users reported problems starting over the weekend, potentially linked to an expired certificate. Google announced a fix is in progress, which requires connected devices for updates, and cautioned that those who attempted factory resets might face additional setup issues. The company is actively encouraging affected users to check their support page for further updates and sharing workarounds discovered on Reddit while the fix is implemented.
We have started to roll out a fix for the problem with Chromecast (2nd gen) and Chromecast Audio devices, which will be completed over the next few days.
A user on Reddit claimed it could be because the certificate baked into the devices expired.
Read at The Verge
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