How can i make the progression from v8 to v9?

As you scale up the climbing grades, progressing from one grade to the next will be more difficult for each new grade. It makes sense that reaching and climbing v9s consistently will be harder and take longer than it did for you to reach the v8s. The same will be for when you want to go from v9 to v10.

If there is a certain project you are working on, try to understand what you are not succeeding in. If it's a specific move, try to practice and train for that specific move until you can do it on the actual route. If it's a difficult hold or body position, train specifically for that.

The point is to break up the route into smaller pieces and to work those out until you can do them on the route itself.

If you can do all of the moves, but have difficulty putting them all together and doing the whole route, try to do it in sections. Try doing half of the route from the start, and the second half from the middle till the end. Or, if there is a specific point that is difficult, try doing the route until that point from the beginning, and then from that point until the end.
Another option is to work a small section with that just point in the middle, so that you are working on that difficult point specifically.

The point with this is to try and improve the moves that you are currently able to do, and to figure out different options for the moves that are difficult.