Reupload own videos

Can I change the status of old videos (make them private) that have not gained views. And then upload them to YouTube again? Can it affect monetization?

If the video was previously monetized, then you will no longer earn revenue from that video while it is private (of course). Once you upload the video again, you will need to reapply for monetization, and it may take some time for YouTube to review& approve but you could make money from it again.

Yes, you can change the status of old videos on your YouTube channel to private if they have not gained views and then upload them again. However, please note that doing so will reset the view count to zero, and any engagement or statistics associated with the original video will be lost.

Yes you can do it, the following text is from youtube website Create & grow your channel.

Replace a video
You can’t replace a video because any new video you upload to YouTube will get a new URL. Instead, you can change an existing video:

Trim your video: On a computer, you can cut out the beginning, middle, or end of your video.
Add cards to your video: You can use cards to add new elements to your video. Cards can show specific websites and more.
Change your video's title and description: You can organize and change your video's title, category, description, and privacy settings.

Thanks for the answers. At this point, I'm growing the channel pretty fast. But some videos are gaining very few views from 1 to 20. So, it would be good to hide them and re-post them, as in my opinion this is very cool content.