Started from the GitHub issue (No longer possible to cast camera after enabling RTSPToWebRTC · Issue #79494 · home-assistant/core · GitHub), where @allenporter suggested to open a feature request instead.
Unfortunately, without this feature, it means that at the moment you enable RTSPToWebRTC integration so that you get low latency streaming, you lose the ability of casting a camera to TV/Chromecast.
The current workarounds I am familiar with is to cast a lovelace panel that contains a webrtc camera with a picture glance card set to a live view.
Note that WebRTC cast support benefits other native webrtc cameras as well, and not just RTSPtoWebRTC.
Just to mention that the suggested workaround does not allow to cast audio. Also, it doesn’t integrate with HA’s media browser, the Frigate Hass Card, etc.
Yes, I’d recommend sticking with LL HLS for those features.
Is it possible to stick with LL HLS for specified cameras in HA once RTSPtoWebRTC is running?
No this is not a per camera feature
Although that’s not possible indeed, the Frigate Card allows you to cast cameras with LL-HLS even when RTSPToWebRTC is enabled.
However, a better option today would be to not use RTSPToWebRTC and use the WebRTC custom integration instead IMO.