Or if you have an old machine and a enough money to by a few hard drives (which you should if you can afford a synology) throw the drives in the old machine and slap something on there. Truenas, Proxmox, unraid, etc. unraids probably the easiest but it costs money. All of them have some kind of docker/kubernetes so you can just run whatever open source version of the thing you want. Nextcloud, libreoffice, etc. you could just install some version of linux too, doesn’t need to be one of those, but those are much simpler to deploy and (most of them) are tailor made for the task
Synology can do all of this too but isn’t as expandable. Want more power to run a jellyfin server and transcode 8 4k streams at once? Plop in a gpu or better yet upgrade to an intel with quicksync for low power usage. Want 8 more hard drives? Change the case and add an hba. Want 24 more? Add another hba and a disk shelf, as long as your motherboard has enough pci lanes. It doesn’t? Upgrade it. The trade off is usability, the synology stuff is easier to use. It’s also more expensive initially, you can make a basic nas with a $50 e waste pc that an office was throwing away (though tbf you’ll probably spend a bit adding disks to it just like you would with a synology)