On Monday, 20 July 2020 10:49:42 UTC+1, Andrew wrote:
There is an aluminium extrusion that I want to use for an LED strip
light. But, it is anodized and I want it painted the same colour as the
wall. It will be inside and 8ft above ground so well out of the way of
any knocks or wear.

What preparation would I have to do to allow it to take Vinyl Matt paint?

I'd try just cleaning it and painting. Remember, the surface of aluminium is actually aluminium oxide - and with anodised, it is a just thicker layer. Any attempt to use acid or similar will either do nothing or affect the anodised layer.

See how it goes on a bit of kitchen foil? The fitting will almost certainly be better.