after catalina install, can no longer access iphoto, how do i recover photos?

iPhoto was discontinued 6 years ago. It is no longer developed or sold. It was replaced by the more powerful (and free) Photos.app that comes with the OS. You can migrate to that app very simply:

Hold down the option (or alt) key and launch Photos. From the resulting menu select 'Choose Library' and point at your iPhoto Library. It will do the rest.

If you prefer not to use Photos there are several 3rd party apps that you can use. Which to choose depends on the kind of photographer you are and your budget.

Here is a user guide for Photos to help you get started:

Photos User Guide for Mac - Apple Support

Click the table of Contents link on this page to see the topics. Some of the pages have a switch to select the system version.