Q.Hibiscus leaves and buds
Hibiscus leaves turning yellow and falling off the plant and also all the dozens of green buds that are on there are slowly falling off . And they’re not ready to open up as yet. Is it over-watering? Under-watering? Or what?

Certified GKH Gardening Expert
Unfortunately, it could be either, as both can give the same symptoms. It could also be a bigger issue, such as rot. I recommend putting dolomitic lime, and wettable sulfur powder. This will bring your pH back to normal. Both of these together, along with proper watering will ensure its survival.Keep the area moist, but not wet or dry. Just in between. Let the soil dry out in the top two inches in between waterings.
Here is an article with some tips on growing hibiscus: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/how-to-care-for-hibiscus-plants.htm