When looking to buy coffee beans from producers that sustain the local forests, waterways, natural wildlife and reclaiming deforested land, as well as farmer friendly practices, which certifications can help me making an informed choice?
There is a report by the International Institute for Sustainable Development which highlights 5 different "voluntary sustainability standards" that are being used. The leading 4 in the report's Production Volumes by VSS section are 4Cs, UTZ (now a part of the Rainforest Alliance), Fairtrade International, and the Rainforest Alliance.
The five standards mentioned in another answer are a good start, but some of them hold little real value. The one that's probably best of the five is Rainforest Alliance, but even that is not immune to issues (see https://abcnews.go.com/US/caffeine-jungle-child-labor-struggling-farmers-found-ethically/story?id=91735230 for recent bad news).
We face this same problem in cacao sourcing for craft chocolate makers. The best solution is harder to scale, but it is DIRECT TRADE, where the roaster buys directly from the farmer in a transparent fashion. The issue with direct trade is the onus is on you to insist the coffee roaster be completely transparent on the trade. Which farm? When? Which harvest? How? Have they visited the farm? Do they continue to visit periodically? How much of that farm's harvest are they buying? If it's less than 100%, ask more questions to see if it's truly direct or through a broker. In cacao, there are some exceptional brokers that are completely transparent, and that can be a good way to go for those buying smaller quantities.
It's a tricky thing that basically boils down to honest, transparency, and trust around the roaster you are buying from.