Let's say I have an external HDD with 4 TB of data, and I store it in the shelf.

There is no dust going into it, or anything.

I take it out from the shelf after 10 years, will it work perfectly in theory? If not, what part can deteriorate and why?

An Internal HDD has the advantage that you can see your data safely all the time, but I'd think that storing the data on an external HDD in a cabinet, or somewhere safe place probably makes the HDD live longer. Is that so? Or not really?

Hello guys, I have about 50 Taiyo Yuden DVDs I bought \~10 years ago, it is still unopened and I didn't burn anything on them.

If I burn stuff on them now will it be in good quality, like new DVDs? Or does the quality degrade even if not used?

I want to burn discs in the best quality, so they don't die within a few years.