Are you talking about Youtube channel videos?
I was also worried about this issue when other people downloaded my videos and uploaded in their own channel and gained thousands of views for free. This was really frustrating and annoying experience. I drove me literally mad few years ago.
But then I realised that we can not stop it!. Yes you heard it right. Moreover there is no need to stop it too. I will explain how -
1) First of all if anybody downloads your videos and uploaded in another youtube channel then youtube will itself identify it and will inform you in the copyrights section of your dashboard. You can then give them a copyright strike for free and put it down. Youtube can put the videos down as well as suspend their account if they are repeat offenders (if they have copied more than 9 videos)
2) Secondly, people can download your videos and upload in other platforms like Facebook and Instagram. While you can not give them copyright strike there, so it is ideal that you publish your videos on other platforms simultaneously on all the platforms. This way you will be the first uploader of that content and will automatically be eligible to give them copyright strike on that platform too.
To summarise, you can not prevent your content from being stolen. You just need to learn how to manage it to control plagiarism across all the platforms.
Hope my answer helped. Thanks.