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.

Your best bet is to use the 3-2-1 backup system and update your backup medium periodically to stay current with technology.
3 copies 2 on different medium 1 stored off-site
There are others that are variants of this but this is pretty secure other than a world apocalypse event when you’ll have bigger concerns.