Do I need to do anything to switch my photos from iCloud to iCloud Photos before June 26, or is this automatic?

If you sign in with Apple ID and its password from a browser at www.icloud.com and download Download iCloud photos and videos - Apple Support

On your Mac or PC

1. On iCloud.com, click Photos and select a photo or video. Hold the command key on your Mac or control key on your PC to select multiple photos or videos. 
2. Click and hold the download button  in the upper corner of the window. If you want to download your photo or video as it was originally captured or imported, choose Unmodified Original. For JPEG or H.264 format — including edits, and even if it was originally in HEIF or HEVC format — choose Most Compatible.*
3. Click Download.

The photos will automatically saved in photo application when you set up photo library Set up and use iCloud Photos - Apple Support and its preferences Change preferences in Photos on Mac - Apple Support

Read Use iCloud Photos to store photos in iCloud - Apple Support

marie-christine241 Said:

"Do I need to do anything to switch my photos from iCloud to iCloud Photos before June 26, or is this automatic?"

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Try Downloading All of iCloud:

Download all of iCloud. Then, search for files through use of Finder on the window to location images of certain extensions (i.e. bmp). Perform my User Tip: Getting a Quick and Direct "iCloud Drive-to-External Hard Drive" Download - User Tip