Argh. Apple makes it so incredibly easy to back up contacts, photos, etc.
They literally do. I have my iPhone 11 synced with my self hosted Nextcloud instance. It works pretty well.
All my iCloud photos are also in /Users/ceejayoz/Pictures. iCloud is a backup and a way to not store ten years worth on your phone. Apple's quite happy to have you have a local copy of it all.
iCloud is the default, not the only option.