Jules, thank you for your help. I added a working example below for anyone who might be interested.
using GLMakie
points = Observable(Point3f[(1, 1, 1)])
fig, ax, scat = scatter(points, axis = (;type=Axis3), markersize = 4000)
limits!(ax, 0, 30, 0, 30, 0, 30)
frames = 1:30
record(fig, "append_animation.mp4", frames;
framerate = 30) do frame
new_point = Point3f(frame, frame, frame)
points[] = push!(points[], new_point)
end