2013 Sony Bravia 70”
That should support 1080p/50 Hz or 60 Hz (use 50 for PAL countries and 60 for NTSC countries).
It doesn’t matter much if you set it to 30 Hz, as most videos will not exceed 30 Hz anyway. Movies and “cinematic” TV shows will often even be 24 Hz (fps).
I would recommend setting Match Framerate on Apple TV, if your TV supports it, to not have two devices make separate video adjustments.
Make sure to use a ‘High-Speed’ HDMI cable (rated 10 Gbps or better), as lesser certified cables may not have the needed support for maximized options.
I tried 720p 60 Hz but that made the screen smaller.
Expected behavior would be for the TV to scale any input resolution to match the screen size (i.e. larger pixels). Verify your TV settings – this is not something that can be configured on Apple TV.