Hello,
Is it possible to get like a glowborder after the over shield and shield like on the picture?

No, you can't

You can create a square indicator (with the the rectangle option enabled) to create a vertical rectangle line aligned to the right of the frame, and link the shields-overflow status to this indicator.

Can you explain your multibar setup ?
I dont understand how is possible to put something after the shields: after displaying a overshield+shield bars, there is no remaining room to display more bars in the multibar, because health+shield amount is a value higher than the maximun unit health.

The picture is taken from using overshield addon on blizzard frames.
I just like there is like an end to the shield multi bar.
That's why I'm asking if it's possible to make so there is a glow at the end.

So you can't anchor it to the shield overflow so it follows the bar?
Atm It only stays where you put the location point.