A lot of these recommendations are for advanced gamers.

Some more entry level games include Portal and journey.

Slay the spire is also excellent if you like card games.

Can it cast to a Roku device?

VPN apps don’t seem to work with it and Proton said their Drive app won’t either. So for whatever reasons those might be.

Not really an answer though. Is it an in house engine? Or a tool made by another company?

Back in the day some iPhones could run janky forms of Android/Linux. I don’t think it ever got to daily driver status but it was surprisingly feature complete.