I apologize if this isn’t the correct place to ask this. If not, just point me to the right place, please.
As per the title, I am looking into backing up files - pictures, movies, music, some documents - locally but with little to mo need of having the backup medium hot. I already have a few HDDs lying around but it reaches a point where is becomes bulky and takes up considerable space.
I’ve been thinking of memory cards because they are reasonably affordable and can be stored away easily. But how reliable are those?
I intend to make/save several backup copies.

Anything magnetic is not good for long term powered-off storage.
Agreed but the way things seem to be moving forward, it seems the MDisc (likewise DVD and BlueRay) technology may be moving towards extinction, as the drives are hard to find and expensive to purchase.
I just bought a drive. They are cheap and plentiful. They are literally used for multi-decade archival. They will go extinct eventually but you won’t be alive to witness it.
An internal drive or one of those external drives?
External. I also have two older laptop drives from different machines that converted to External.
If you’re really paranoid you can export the data to different media types including archival dvd and archival tape. Tape is unreasonably expensive for SMB/home use though.