Hello Andre, interesting question, there is not really an official optimization number that Google shares with you, related to Google Shopping, but there is for Text ads, and there is a quality score for PMax assets.
So I’m unsure what you meant.
However, if it’s Google Shopping, a great tip would be to improve your data feed quality by following the requirements and recommendations here: https://support.google.com/merchants/answer/7052112
If it’s for text ads and pmax assets, then I recommend ensuring your landing page is optimized, meaning having great content, that the consumer wants to read.
And then have headlines and descriptions that highlight what you sell, and also include things such as how many reviews you have, what sets you apart from the competitors etc.
For image assets, try different sets of images, such as lifestyle images, images with great catchy text, etc.
I hope this answers your question.