Oh no, I don’t think it would be able to pull from iCloud directly, I believe there is an option to delete uploaded photos on the iOS device after uploading in the Nextcloud app but I don’t know if that is automatic or requires the user to acknowledge a prompt unfortunately.
This isn’t necessarily a 1:1 answer for you but it’s just what I have experience with: I used Nextcloud for a period of time and set up the app to upload which worked like any basic cloud storage service but what I’ve done since (I downsized) is just use the PhotoSync app and it’s companion on my PC. You can target a PC (like I do), WebDAV, FTP, SMB, etc. which may help with scalability.
The Trust Thermocline!
This I wish, but I doubt. I still have my old Garmin GPS and play with the idea of a flip phone but I’ve been spoiled by the smaller things like iMessage not dealing with MMS. It’s an idea I come back to occasionally, but I also think about going back to my Palm with AAA batteries for my PIM needs. Had one in semi-regular-use as recent as 2018!
Don’t worry all, the FAQ has reassured me that you can still use offline features like… checking the battery level!