Hi Jayc89,
Many brick slips suppliers have a carrier board / recommended fixing detail.
For instance Eurobrick V clad or X clad, who have this panel to slot the bricks into https://www.eurobrick.co.uk/v-clad the carrier board is screwed into the ICF fixings.
Also have a look at https://www.ribaproductselector.com/Product.aspx?ci=16545&pr=Wetherby-Brick-Slip-Cladding-SystemsWBS15mmBrickSlipCladdingSystems These are fixed to their crimped steel mesh which is also secured to the embedded fixings in the ICF blocks.
There are many others including Ibstock, Brick slips Ltd etc. I would be looking at a system that has a backing panel or similar as they are much easier to install than ones without carrier systems.
However, without a carrier board, you can attach brick slips to a render basecoat. It's just more difficult to ensure straightness.