How to make billboardgui which isnt resizing when Im going further?

Just set the scale of the BillboardGui's size property. Setting it to full scale (i.e, {1, 0, 1, 0}) is roughly in proportion to the size of a single stud, so you'll probably want to set this value several magnitudes over the limit. In the gif I showed you, the dimensions were: {10, 0, 10, 0}. Your frame, or whatever GUI object you have inside the BillboardGui, should be set to full scale so it stays in proportion to the BillboardGui's size.

Result yielded

Well, for that your Billboard Gui's Adornee(Parent part) gotta be in Player's Local Camera, so it gets smaller for one player while it's still big for a player which is closer.

Now, let's say there are limits we put and also sizes for these limits.

Limits = {0,30,50,100} --studs far away
Sizes = {(0.25,0,0.25,0),(0.2,0,0.2,0),(0.15,0,0.15,0),(0.1,0,0.1,0)}

Then, let's get Camera's position, and also parent of our GUI

Ador = game.Workspace.CurrentCamera.BillGuiPart
CamCFrame = game.Workspace.CurrentCamera.CFrame

Now, a small if condition to get distance between Camera and Ador And also a for loop

for i = #Limits,1,-1 do
    if (CamCFrame.p-Ador.Position).magnitude > Limits[i] then
        Ador.BillboardGui.Frame.Size = Sizes[i]
    end
end

This will take care of sizing I think. I do not 100% guarantee.