when updating to mac os catalina lost my photos

Where is your iPhoto Library stored? If you are keeping the iPhoto Library on an external volume, you may want to check, if this volume is suitable for a Photos Library. he requirements are listed here: Move your Photos library to save space on your Mac - Apple Support

Did you migrate the iPhoto Library?

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.