On mac:
System drive -> 4TB USB-C SSD via Carbon Copy Cloner, changed files every 2 hours, refresh everything every week, with snapshots.
Anything I can store on an external, I do, on a second 4TB USB-C SSD (I don't like Apple's internal storage design and use it as little as possible).
Folders on the root of that drive (e.g., documents, music, movies, photos, big-picture folders for my day job and my music job, etc.) get backed up to a NAS, also via CCC with snaspshots and occasional refreshes, automatically. The schedules are based on how often I actually change things in them. My current NAS is a Synology and has a big mdraid+btrfs RAID10 in it. Some time this year, I'm probably going to switch to using a FreeBSD VM on my home server (not TrueNAS, because TrueNAS is crap).
The NAS actively syncs my stuff to Backblaze and day job stuff to Google Drive (we use Google services enough that I think we're up to 200TB of Drive storage...plus, it's their data anyway).
When I was on a PC, it was the same idea, but the external drives were network shares via 10GbE to a storage server. I quit doing that when I switched to macOS because for whatever reason Mac doesn't get anywhere near the latency or throughput performance that Windows, Linux, or FreeBSD do over 10GbE. It was noticeably slower working off the storage server than a local SSD, but only on macOS. And, no it wasn't the array in the storage server; that was all flash. The only spinning hard drives I still own are the ones in the Synology. IDK...maybe there's one in my PS5, I didn't check because I don't care.