1) SSDs and flash memory need to be refreshed (rewriting all the same files) at intervals of 1 year or more to keep the data intact and free from corruption and bitrot.
Do 2.5" and 3.5" HDDs also have this problem? Even if the drive is in good health, if the data was written many years ago, are they at risk of corruption, loss of magnetism, bitrot, and other problems?
generally i acess energize my drives 1 once year more no nothiting write

2) Do 2.5" HDDs for long-term storage require specific, perfect conditions of 50% humidity and 25°C? Is oxidation and corrosion possible above that?

In My home varies in 24h 33-38C 55-66%

bit rot is worst with SSD while hard disks is somewhat less problematic. I keep hard disks in USB enclosures while my various laptops have M.2 SSD installed.

I have many laptops and they boot up fine after sitting on a shelf. So far no issues but sometimes Windows gets mangled by so many updates so I sometimes start fresh.

I have an Orico 5-disk enclosure and several other USB enclosures. I have trashed some old enclosures as they had LBA22 or LBA24 limits and as hard disks grew bigger the old enclosures were replaced to handle them.

Now I have a bunch of old laptop hard disks and they worked when checked after 4 years. I am not sure how long they can last but I suggest USB enclosures and USB hubs can be used to power up lots of disks so they can refresh weak sectors etc.

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Orico DS500C3-US-BK 5-disk 3.5" SATA, iTGZ 4x M.2 2280 Thunderbolt enclosure NVMe/SATA, etc. etc.