Quick answer is to use google chrome browser casting feature, and cast it to new tab, not desktop or youtube app. Cast it to your new tab of google chrome browser.
First most important thing is to update your google chrome browser. Normally you will see an arrow up red on the top right hand corner of your chrome browser, click on it if you see it, your chrome browser will get updated. Another way is a manual way to be sure it is latest version by going into the settings and go to About Chrome and it will do a thorough check to make sure your browser have the latest update. Always keep it automatically updated.
Next thing is use a desktoptop computer or if you have a fast laptop notebook computer that’s fine also, because if you have a slow computer or slow internet wifi then this will not work well, you will see lagging and buffering. So it’s best to have a good computer and good internet wired instead of wifi if you can otherwise lagging and buffering is inevitable.
Now you can visit any website that have videos movies that you want to watch, simply click on the cast and then select cast to tab to the device you have. Now you can minimize the browser but notice that your casting device or TV is still playing, isn’t that cool? you can now also do other stuff on your computer while the casting device or TV remain interrupted of your videos or movies.
TIPS: enable ads blocker and youtube ads blocker to enjoy uninterrupted videos or movies. This is something your android or ios youtube app cannot do. Android IOS youtube app, there isn’t a way to disable ads playing on your youtube videos and other cast enabled movies video either. So it’s best to use you google chrome with the ad blocker and youtube ad blocked enabled and enjoy endless movies videos not interrupted and keeping your chrome browser and computer safe from spam ads advertisements viruses and malware.
Another tips is to use your wired network cable instead of wifi on both the casting devices (your computer and your tv) This will make casting smooth flawless especially for HD 4K 8K videos. This will also allow your home or where ever you need some bandwidth for your other wifi users or other devices that required wifi only like your tablet and phones.