I read the firmware change notes. There is no mention of battery level indication. I also reviewed the D7500 online user manual. There is no option I see in the custom settings menu or the photo shooting menu to turn the battery level off in viewfinder.
Like pretty much all of the display in the viewfinder, you should wake up the camera to show the full display inside. Typically you should try a half-press on the shutter release and see if the battery level then shows on the bottom-middle-right area of the viewfinder.
Other options to consider: Aftermarket EN-EL15 battery might be detected on newer firmware and the level data ignored. If you are using an aftermarket battery that is. Did the D7500 have a battery grip option? Thinking remove that if applicable.
That too is what I though. I too read the release notes prior to upgrading. I looked at the manual and, as you say there is no mention of bttery icon options in the toolbar. I even looked and my Nikon D7500 for Dummies book for help.
I removed the battery for a full minute, put it back, powered the camera on and what I see in the toolbar when I take up first pressure on the shutter release button is, from left to right, a white dot indicating focus, shutter speed, aperture, ISP/AUTO [r99]. r99 is a buffer number, I think. That's it. but, the battery is not an OEM Nikon. The original long since died. What is in there now is a Neeweer LiON type. I have two mpre 3rd party batteries on order from AMazon and they will be here tomorrow. I do not have a battery grip option on the camera.
I am puzzled.