I paid for 1Blocker (https://apps.apple.com/us/app/1blocker-ad-blocker/id1365531024) since it runs locally on my phone to block ads as well as trackers from other installed Apps, whether on my home WiFi, other WiFi, or cellular data. There’s a whitelist feature and the filtering can be tailored. I’ve been using it for years (before I got my current phone) so I can’t comment on battery life but I’ve never noticed it to be bad.

It does break some apps if they’re not whitelisted but that just gives me more reason to decide if I really need the app. It’s also possible to temporarily disable the blocking (5 minutes, 30 minutes, etc) which helps with logging in (since so many login services involve trackers).

Is there a way to have multiple users on one device with different lists of subscriptions? Or be able to toggle between different lists of subscriptions?

If Apple chose to use a 16-bit integer for the index, they would be limited to approximately 65,000 photos. 32-bit would be about 4 billion. Photos likely uses a 32-bit or even 64-bit integer index value to make it a non-issue.

There could be issues with having too many thumbnails loaded in memory. Maybe some other value overflows when scrolling through (or just loading) an enormous library. If Photos also creates an index for searching that could also create headaches. If Photos were a simple file explorer having a million files shouldn’t be an issue but it’s more than that, so it’s good to know it seems to be performant with even 1 million photos.