Error occurs (Screen AirPlay + Multi-room speakers)

I have Samsung Smart TV, Apple TV, Home Pods mini(x2), and Sonova Wi-Fi speakers, and iPhone.

I controlled my iPhone to Airplay a video of Apple TV+ to Samsung TV via Apple TV and then, controlled my iPhone again to enrich the sound by connecting(air playing) multiple speakers (Home Pods~Sonova). However, the screen was turned off to the black screen and only the sound was played on multiple speakers. How can I fix this?

An interesting thing is that connecting(air playing) multiple speakers is enabled very well when I try that by controlling Apple TV not iPhone. In conclusion, you can connect multiple speakers through Apple TV device but can't connect through iPhone while air playing videos. Is it normal? or Do I have to change some settings?