How can I put my private and hidden photos into my Google Photos?

Best check with Google for assistance with importing data.

Here is the import doc: https://support.google.com/photos/answer/11828494?hl=en

I would not consider any photos loaded into Google Photos to be private, given Google exists to collect and aggregate data and to use that for various purposes including selling targeted ads.

But check the Google service terms and conditions for details ofmwhat will happen.