The fuck bullshit take is this, LOL.
Not trying to fanboy or any bullshit like that, but it’s up to the app developer to release compatible versions of their app for different devices.
WhatsApp is to blame for no WhatsApp on Apple Watch, not Apple.
Settings > [your name] > iCloud > Manage iCloud Storage > Photos > Disable and remove from iCloud
Be aware that if your photos are on your iPhone when you do this without having previously downloaded the originals and disable iCloud Photos, it will delete your photos from your iPhone as well.