Chromecast unable to find TV

[asb3]

I want to use chromecast to display media (or desktop, if possible) on my TV. I have a TV with built-in chromecast.

I can share my android tablet screen using an app called "Screen mirroring stream". The app sees my TV, which is on my local network.

I have chrome, VLC, and mkchromecast installed on my linux box (running Ubuntu 20.04).
From Chromium, when I select "cast", I get the "Cast Tab" with the message "Searching for devices". After a few seconds, I get the message "No devices found".

Running VLC, I have a similar problem
Playback->Renderer
only gives one option, "Local".

Running mkchromecast, same problem:
(base) asb@cavu> mkchromecast
Mkchromecast v0.3.8.1
Creating Pulseaudio Sink...
Open Pavucontrol and Select the Mkchromecast Sink.
Starting Local Streaming Server
[Done]
Selected backend: parec
Selected audio codec: mp3
Default bitrate used: 192k
Default sample rate used: 44100Hz.
* Serving Flask app "mkchromecast.audio" (lazy loading)
* Environment: production
WARNING: This is a development server. Do not use it in a production deployment.
PID of main process: 7096
Use a production WSGI server instead.
PID of streaming process: 7102
* Debug mode: off
* Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)
No devices found!
Cleaning up /tmp/...
[Done]
Killed

What do I have to do to permit chromecast to see my TV?

[crip720]

Would try with Chrome instead. Google does something so that only their products work well together. Only have chrome for videostream app that seems able to play/convert easy to chromecast. Other casting apps seem to really work my laptop trying to cast to chromecast.