iPhoto on external hard drive after Catalina update

Before I upgrade to Catalina, I want to make sure I can still access my iPhoto library which is stored on an external hard drive. I read that I can just use Photos to open the iPhoto library. Will this still work on an external hard drive?

Will I need to migrate my iPhoto library into Photos? Or can I just rely on Photos to view my iPhoto library in the future?

Thanks so much in advance for any advice!