You should follow in the steps of Linus Tech Tips and build a massive file server. That's probably the most comparable system and situation to your case.
Ex
https://m.youtube.com/watch?v=pLC0FUnko-M
https://linustechtips.com/topic/1447503-this-is-my-endgame/
I'd then recommend tape backups that you store off-site , maybe backblaze , but as others stated that might be too expensive.
For 20 TB of computer measured storage you need a 22 TB hdd. ( Due to the way hard drive manufactures market vs how computers read disk size, they use different base systems)
I recently got 20 TB Seagate EXOs for $260 on eBay sold new by Newegg .(20 TB EXOs has 18 TB usable as read by Windows and Linux )
HDDs are getting cheaper at the high end.
SSDs are still new enough that they are still figuring out how to get economic viability where HDDs were a decade ago.
1TB for $100 is new in NVMEs for example.
Lol, I'm not using windows for this. If I never see windows server again I'll be happy.
I'm probably going to go Unraid, more research along with some posts haven't actually found anything better at this point. Maybe that company LTT invested in will one day release something.
The only other good option was truenas, but it doesn't seem to meet my multi drive size spec well. ( Without some jankness that would impact my want for low maintenance)
I have 4x 10 TB WD reds white label I shucked from WD nas boxes.
I also just picked up 2x 20 TB Seagate EXOS drives new for $200 ish on eBay sold by Newegg because I need to very rapidly find a solution for my 18TB unlimited Google drive that is going away in December.
I found some reasonably priced new newegg ( sold on eBay) 20 TB Seagate drives recently.
I just bought these after a few weeks of research. I have to download and dedupe my Google drive before uploading back into my NAS ( and deduping there too)
20TB 7200 RPM 256MB Cache https://www.ebay.com/itm/384674693043?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=Ok6NaWEKSPa&sssrc=4429486&ssuid=uM5KnkqCS4q&var=&widget_ver=artemis&media=COPY
This is specifically the high capacity storage system. They don't Experience failures with that. LTT does hype up things as failing but it's not their essential stuff.
It's not just them that use these either, there's also companies like 45 drives
https://www.45drives.com/products/cluster/configure/