can iPhotos be converted to photos?

That is correct - on a Mac with macOS 13 Ventura the Photos.app can no longer convert iPhoto Libraries to Photos Libraries. The last system to support this has been macOS 12 Monterey.

On macOS 13 Ventura you can import the photos from the iPhoto Library into an existing Photos Library as described here: Import photos from another library in Photos on Mac - Apple Support. This will give you access to the media inside the library, but you will lose the structure of the library - the albums, folder sand events.

Just open the Photos Library, where you want to add the items from the iPhoto Library to (or launch Photos and create a new Photos Library), then use the command "File > Import" and select the iPhoto Library. Photos will now show you all photos, that have not yet been imported to the current library.

You may also want to look at this user tip for details: Importing photos directly from another Ph… - Apple Community

Or do you own iPhoto Library Manager or its successor PowerPhotos? On macOS 13 PowerPhotos can convert iPhoto libraries to Photos Libraries. This will help you to save the structure of your iPhoto Library. But you need the full, paid version of PowerPhotos. http://www.fatcatsoftware.com/powerphotos

Hold down the option key while opening Photos.

Then, point to the old iPhoto file for conversion to Photos.