I was thinking about making another channel on YouTube for watching movies, for example when I travel and don't have my laptop with me. As far as I know, people can get copyright strike for uploading as public content they don't own.
However, does this apply even when I set this copyrighted content (movies, TV shows, etc.) as private, so nobody except me can watch it?
Reasons why I want to use YT is great buffering speed, no ads and good mobile app.
Yes, you can get a strike.
ContentID (an automated copyright detection tool) is scanning all videos, regardless of privacy status, and while it can't strike* you directly, it can block the video and tell the copyright holder "look, here's a private video that you can't see, but I'm 99.9% confident that the part from 0:00:00 to 2:21:13 is your movie. Do you want to strike it?" — and if the copyright holder says yes, you have a big problem.
What you may want to do instead is use a service like Google Play Movies or Netflix – though I don't know how nice either of those are in terms of geo restricting users.
* sidenote: "strikes" are actually legal DMCA takedown notifications (as per 17. U.S. Code §512 (c)(3)(A)), copyright holders generally don't want to send out those automated because they can be held liable for abusing them
