It's good having a south-facing garden but the sun can take its toll on
materials exposed to it.

I have a small area (about 3sqm) of timber shiplap cladding that has
seen better days (peeling paint and weathered wood) and would be simpler
to replace [1] than refurbish. Replacing like for like would give the
same problem in a few years. The question is, what would be the best
material for a 'fit and forget' solution?
Thoughts so far include:
Varnished hardwood - would still deteriorate in time
uPVC shilap - shiny white wouldn't look good and creaks nadtily when it
expands in the sun, but I can't see any sensible info on how well the
darker foil-faced versions last.
Fibre cement cladding - plenty of finishes available but seems to be
painted, not coloured throughout the thickness, so would possibly give
the same problem again.
Bricks - a lot of faffing to do, given the location, and I'm struggling
to source bricks that match the house for other purposes.
Synthetic slates - should be pretty sun-resistant but may be challenging
to hang vertically.

In the US, they use aluminium 'siding' that lasts well, provided it
doesn't suffer any impact damage. I've never seen it in the UK.

[1] As I'm in a conservation area, I really shouldn't have any sort of
cladding anywhere, apparently (wtf is that rule about?), but I don't
think anyone will notice on a like-for-like replacement at the back of
the house.