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Before you just restart it, try forcing a network settings reset in the Nest app (settings > reset network) - often an update just kills the wifi connection, not the thermostat itself. If that doesn't change anything, then you can go ahead with a full restart.
It's not necessarily the update that's causing everything - sometimes it's just a bad sync 😅 Try doing a complete restart first by turning it off and back on, then check that your wifi is stable and the Nest is actually connected. If that doesn't help, reset it through the app (factory reset), that fixes a lot of weird stuff. If it's still acting up after that, hit up Google support, they're pretty quick to respond with this kind of issue.
I had something similar where the Nest was displaying completely off-the-wall temperatures after an update, and I had to check that the internal sensor wasn't clogged or blocked by something silly - sometimes dust or a spider web in the vents totally throws off the detection. If it's really tied to the update itself, you can also try rolling back to the previous version through the app (settings > device info > rollback), though that's not always possible depending on your model.
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