I've updated to the new iOS 26.4 & tvOS 26.4 betas, and am finding both to be pretty awful!
iOS - I run a dual sim set up, with my US number on eSIM and UK on a physical SIM. Ever since updating, I can no longer send iMessages from the US number. I have forced restarted, switched number activations On & Off multiple times - nothing works. I really don't want to have to run Reset Network Settings, but that seems to be my last resort. Hopefully the Beta 2 will fix this.
tvOS - Media can no longer playback Dolby Atmos from any my apps (TV, Disney+, Netflix, etc). I just keep getting errors that there is an audio playback issue. (Running the Apple TV into an HDMI switcher, going to a Sonos Arc Ultra & a XGIMI Horizon 20 Max Projector). The only way I've been able to get around it is to go to Audio Settings, and switch "Change Format" to "On" - and then it converts all audio to 5.1, and I can play media again. But this is not ideal!