What is the best way to automate background database updates of a front-end app?

I have a JS app (deployed on Vercel) where users can leave reviews of places. What I’d like is, when you open a place’s page, to see the number of reviews and the average value of those reviews. But I don’t want to do this query on that page (to gain load speed). And I also don’t want to do it when submiting a review (also so the user doesn’t have a big load).

I first tought about a serverless function which would be trigerred upon submiting a review. But how could I trigger that function without the app having to wait for it to be done? It would run in the background not blocking the app