While iCloud with ADP is end-to-end encrypted, they don’t encrypt the metadata and checksums.
Some metadata and usage information stored in iCloud remains under standard data protection, even when Advanced Data Protection is enabled. For example, dates and times when a file or object was modified are used to sort your information, and checksums of file and photo data are used to help Apple de-duplicate and optimize your iCloud and device storage — all without having access to the files and photos themselves.
Not (e2e) encrypted for iCloud Photos even with ADP:
The raw byte checksum of the photo or video
Whether an item has been marked as a favorite, hidden, or marked as deleted
When the item was originally created on the device
When the item was originally imported and modified
How many times an item has been viewed
Source: iCloud data security overview - Apple Support
For most people that would be fine, but you need to decide to for yourself. I think the checksum is particularly worrying. Unless I’m misunderstanding it, they could compare it with a list of “forbidden” checksums. Not even talking about CSAM, it might be just scanning for people who have saved an unwelcome political meme.