I currently have Google nest Wi-Fi and I was about to upgrade to deco mesh. In Google you can share devices like a tv or chromecast with people on your guest network following simple instructions here: https://support.google.com/googlenest/answer/6327302?hl=en

Unfortunately all my research led to an understanding that this is not possible with Deco. This is a show stopper for me. If I am wrong please let me know. Without this feature i'm sticking with Google!

Here are all the articles I found:

https://community.tp-link.com/us/home/forum/topic/256974
https://community.tp-link.com/en/home/forum/topic/570346
https://community.tp-link.com/en/home/forum/topic/622938