I keep all documents I deem worthy, forever. This might become a problem after a few years but for now hasn't been an issue at all. Search is quite powerful for documents in particular.
One system I do have for documents which has been very useful is the one I describe here.
I like to keep as little media files as possible. Especially when it comes to family photos and videos. It's super easy for these files to balloon to crazy sizes quickly. I can easily delete 50% of the photos and videos that I take. People tend to cite how cheap storage is as an excuse to keep all data - storage has advanced quickly but search and data transfer speeds haven't.
That means that you might cheaply have 4tb of photos and video in a disk but if you want to transfer a subset (say 10%) of those files it could be a day of work. You might be doing that for photos and videos that you won't be happy to look at anyway!
Have you ever downloaded 200gb of data from the cloud. Before you start talking about he convenience and prices of the cloud - try doing that. I have gone through that process and can tell you that on that argument alone, I won't be backing up in the cloud.
In the EU you can buy 2Tb of storage for about 120 EUR. I have an old laptop which you can buy for less than 100 EUR used. I have this laptop connected to the disk and I use Tailscale to create a VPN to be able to access to that laptop from anywhere. I have two of these machines, one at my place and another at my parent's place who live close by. I keep both of these drives in sync using rsync. This allows me to have offsite backups that I can easily access physically if needed. Both the drives are encrypted using LUKS.
This is not the most automatic or easy way to back things up but it's the most useful in my opinion. It's the kind of backups that you can actually use. Also, what is nice is that if you are not technical, you can forget tailscale, LUKS and rsync and just back things up on your laptop using your local network or even just plugging in another drive to your computer.
There are a lot of companies making a lot of money by convincing you that you need something other than a cheap laptop with a big 2tb disk attached to it.