I think this was addressed here How to add grid lines on top of a heatmap in Makie? - #2 by jules
So basically just:
using CairoMakie
fig = Figure()
ax = Axis(fig[1, 1];
xgridcolor = :white,
xgridstyle = :dot,
xgridwidth = 10,
ygridcolor = :red,
ygridwidth = 10,
)
hm = heatmap!(ax, rand(5, 5))
translate!(hm, 0, 0, -100)
fig
A bunch more options can be found here API