I've wondered that myself for some time. Looking at the switch matrix chart, my guess would be it's the "Score 500 Round Target":
Screenshot_20211116-084948.png

Looks like it just scores 500 points.

It also lights the spinner and advances bank shot one unit.

I believe you are thinking of the target at the top right. The OP is referencing the target at the top left.

Oh, yeah. I thought you meant the rectangle target. Sorry. Not sure if the round red one does anything beyond 500 pts.

The top left small round target scores 500 points.

Top top right rectangle target scores 500 points and lights the spinner for 1,000 points a spin. It also lights the kickback for the left side drain, which turns off and needs to be lit again after a kickback.

To score and advance the "Bank Shot" bonus multiplier amounts all the way until an extra ball, you need to make the horseshoe shot over the star rollover. You can also advance these by completing all four lanes at the top of the playfield and then hitting whichever of the middle two lanes are lit.

After completing the lit seven balls the top right target lights for the "8 Ball". Hitting this while lit gives you a "Super Bonus" on the next ball, which holds over until the end of the game.

Bonus multipliers and lit spinner shots all day in this game! Great shots and a great game when dialed in and playing fast. A waxed playfield and tight gaps on the pop and sling switches make this game fly.