THM can't be decoded
THM is a proprietary/undocumented format that no image library or converter can decode, so it can't be read as a source file.
Trying to turn a THM into DDS? Here's the honest answer — THM isn't a readable image format — and the steps that get you a real picture.
We can't convert THM to DDS — an THM file can't be opened by any converter. Here's why, and what actually works.
THM is a proprietary/undocumented format that no image library or converter can decode, so it can't be read as a source file.
Because nothing can read the THM container, there's no image data a converter can extract and re-save as DDS. Any tool that claims to do it would just fail.
The real photos an THM cache was built from live in your photo library or a backup. Export those (they'll be JPG or HEIC), then convert them — that's a conversion that works.
THM is a small JPEG thumbnail saved alongside camera photos and videos — really a JPEG with a different extension.
How to open Rename or convert THM to .jpg to open it anywhere.
Full THM format guideDDS (DirectDraw Surface) is Microsoft's texture format for games and 3D apps, storing compressed images with mipmaps that GPUs read directly.
How to open DDS opens in game engines, GIMP (with a plugin), Photoshop (with the NVIDIA plugin) and texture tools; convert to PNG to view normally.
Full DDS format guide