I don’t think that they are LEDs. Looks more like electroluminescent wire aka EL Wire.
https://en.m.wikipedia.org/wiki/Electroluminescent_wire
Could be useful to put the ambient lighting in the rear doors, something I have wanted to do, to match the front. Although you will be limited to one colour, and need to get it to work with the headlights coming on...
Also make a good additional boot light to brighten up
Just a thought, more practical uses....
nice spot, saved this for later.You can buy that from AliExpress.
It's just EL wires fitted inside a special jacket with an extension that you nudge between panels.
It can be trimmed to the size you need, then just tap any 12V source, preferably something that matches the light conditions of your dash instruments, and you're done.
https://www.aliexpress.com/item/32800905365.html
You could use the feed that is used to illuminate the rear window switches to get strip to come on at the correct time