It sounds like you have the newest thermostat model, with the mirrored face, which doesn't have a setting to manually change the brightness unfortunately. This is mostly a user to user community, therefore if this is important to you, I’d encourage you to also send this feedback directly to Google. You will not receive a response, unless Google need more details from you, however the team are still reading the feedback.
I assume I just need to get a different thermostat than my Google Nest. It is troubling as it is brand new. At night it auto-dims to the point you cannot see the screen unless you turn on lights in the house.
I just wanted to jump in and confirm something real fast. Is the Nest Thermostat model you're using the newer model with the mirror finish, or are you using a different model? Depending on which Nest Thermostat you have, you may have options for handling the brightness of your display. Let me know which one you have and we'll look more into it.
I am sorry to hear you no longer have the Nest Thermostat. With that being the case, we are unable to troubleshoot further. Please let us know if you have any other questions from here, as I would be happy to take a closer look.