Trouble accessing old iPhoto library
I have a Macbook purchased in 2007 running OS 10.6.8. I have almost 10,000 family photos stored on this Mac. I backed up the iPhoto library to an external drive. When I try to open the backup on my 2015 MacBook Air running 10.15.4, it tells me the library cannot be recognized. (I pressed the option key when opening iPhotos where I selected the desired library). Can anyone help? Thank you!