I have solid 720p video 30fps video, no problems.
You don't need a capture card unless you want better than 720p30fps. (Then again, I have no idea about the linux/windows situations)
But use Camera Live v11. (Newer versions hit some problems with Catalina)
And tweak CamTwist settings to do 720p 30fps. Browsers won't acknowledge CamTwist new/changed virtual cameras until you restart them.
I have solid 720p video 30fps video, no problems.
You don't need a capture card unless you want better than 720p30fps. (Then again, I have no idea about the linux/windows situations)