Moving iPhoto library to iCloud
I'm in the process of retiring a 2010 iMac and moving to a 2019 MacBook Air.
Since there is a disparity in hard disk size between the iMac (500GB) and the MacBook Air (128MB), I would like to move my photo library to iCloud. The photo library is the main thing on the iMac that I'm worried about storing - everything else I can work around.
My plan was to copy the iPhoto library (~135GB) from the iMac to an external hard drive and then open using Photos on the MacBook, to upgrade the library to Photos format and then sync the library into iCloud.
Moving the iPhoto library onto the external drive worked but when I open the library using Photos on the MacBook, it just says "Preparing Library 0%". It's stuck like this for >1 hour. I've tried this process several times with no progress. I've rebuilt the thumbnails and repaired the permissions on the iPhoto library on the external hard drive but this hasn't helped.
Does anyone have any advice on my general strategy for moving the library to iCloud? Am I missing something here? The external drive is also quite old ~2011, I think it's USB 2. Will this have an impact on the process (other than just transfer times)?
Thanks
MacBook Air