The only way around Using YouTube on the old NowTV boxes, from as far as I can tell, is to use your mobile phone's YouTube app to control the content on your smart box.
1: Open the YouTube app on your smartphone
2: Press the cast icon in the upper right corner
3: Select your smart box eg RokuLT...
4: Use your smart phone to select videos on YouTube to play on your smart box
If you use your smartphone the box barely crashes, probably once a day, if that.
Hope this helps
This is good but obviously you're not good enough