My MacBook Pro had iPhoto app forever. Then one day it was gone. I have thousands of images stored on it. How do I find them?

There are articles that look helpful to find iPhotos content, for use in later Photos.

Some of these articles have great comments too, & some, not so much.

• How to access your old iPhoto library without iPhoto | Macintosh How To

https://www.macintoshhowto.com/software/how-to-access-your-iphoto-library-without-iphoto.html

• How to Recover an Old iPhoto Library | lifehacker

https://lifehacker.com/how-do-i-recover-an-old-iphoto-library-1829215169

• How to Move an iPhoto Library into Photos for Mac - OS X Daily

https://osxdaily.com/2015/04/17/move-iphoto-library-to-photos-mac/

An extensive article, a user-tip from an expert in Apple community, worth saving:

• Notes on Migrating an iPhoto Library from iPhoto to Photos for Mac | Apple Community

https://discussions.apple.com/docs/DOC-8461

• Find your pictures or albums after you migrate a library to Photos - Apple Support

https://support.apple.com/en-us/HT204887

• Tips for moving from iPhoto to Photos for Mac - Macworld UK

https://www.macworld.co.uk/feature/move-iphoto-to-photos-for-mac-os-x-3586301/

• Move your Photos library to save space on your Mac - Apple Support

https://support.apple.com/en-us/HT201517