Mixed device household - Needing help with storing photos and backups

Good afternoon all, I have half-assed my backups for 15 years, and it is not sustainable, and I need your help! I have the following setup: 1x Raspberry Pi 4 with a WD USB3 MyBook 4TB as a NAS target using OpenMediaVault. This works well enough, but is not in my mind a long term viable solution. 1x Apple Airport TimeCapsule...