Can't convert Iphoto Library on External Drive to Photos

Hello, I held off updating to Monterey, but now that I've done it, I no longer have access to Iphoto.

I have several large Iphoto libraries on external drives that I want to use in Photos, but when I try to open them in Photos, the conversion stalls generally when the progress bar gets to about 9%. I have successfully opened an Iphoto library in Photos that was on my hard drive, but I don't have space on the hard drive to move the libraries from external drive and open that way. Any suggestions short of going back to an earlier IOS? Is there away of just importing the photos into Photos, rather than converting the libraries?

Second question: On the library that I did successfully convert that was on the hard drive, none of the videos in the new Photos library had thumbnails. The videos are there, but in the Photos library they just display with a blank, back square Any ideas?

Thanks