As you are reporting problems with Photos Mac and not Photos iOS, I'll ask the community hosts to move your question to the Photos for Mac Forum.
if you are having repeated crashes and Photos is hanging and cannot be quit, you may have items in your Photos Library that are incompatible with Photos 5 on Catalina, for example older videos, in a format, that is no longer compatible with Photos.
You may want to check your Photos Library systematically for photos and videos, that may be in an unsupported format, photos you imported while still running iPhoto or Aperture. Remove PDFs, BMP files, PICT files, audio files, any videos in a format, that are listed here as incompatible with iMovie: About legacy media in iMovie for macOS - Apple Support
They might be causing trouble in Photos 5 as well. Incompatible media should have been weeded out and converted before upgrading to Catalina and Photos 5. Now it is more difficult to convert them, because Photos 5 can no longer process them: If you can't play videos in Photos on your Mac - Apple Support