Honestly your best bet is probably get a Chromecast. From the sound of things the TV may have not properly implemented the Cast API.
Do you have ad blockers ?
Make sure the TV and other device are on the same wifi. That may include making sure they're on the same band (ex. 2.4GHz or 5Ghz).
Downgrade Chromecast and the remote control app on the TV and turn auto update off. Had the same problem and this fixed it for me
I got my main router and mesh system my TV is connected to main router but my phone jumps around on different access points so have to make sure it's on main to cast to tv
Have you try updating Cast and Casting app on your mobile?
Refer the video description:
https://m.youtube.com/watch?v=_zGwXrA6MWE
In case OP is still having troubles I was / am --- turns out it is specific files that Chromecast will not play. those include MKV , HEVC and VP9 (whatever that is )
I'm trying to figure out why my casting is intermitant ... this is the leading culprit.