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.

I looked up MDiscs and they are pretty stupidly expensive but might be a reasonable bet. You might want to use something like PAR to make a backup, that gives you some redundancy without making extra copies.
From experience I can say leaving HDD’s powered down for long periods is asking for trouble. The lubricants in them get sticky and then the drives won’t spin up. Ideally you want to keep your HDD’s spinning all or most of the time.
I guess you could check ebay for an older generation LTO tape drive. LTO 5 isn’t a total relic yet, and it stores 1.5TB on a tape, which would give you a bit of headroom above your 1TB dataset. Tape and optical disc are about the only backup media with any durability.
If your media files are of public interest and not in copyright, you could upload them to archive.org which is free, and other people could access them too.