Spots on Luna Hibiscus and yellowing leaves dying

Question

My Dwarf Luna Hibiscus plants were gorgeous until about a month ago. I admit I planted them about 6″ too close together 4 years ago. And they have multiplied – making a neighborhood statement when flowering (lots of compliments and people asking for seeds).
The spotted leaves sometimes go fully yellow (then brown) – down the center/middle of leaf first. Then entire leaf does.
I have tried a couple fungicides, but one was a preventative 3-in-1. The other Propiconazole. No impact. Hoeever, I could not spray all the leaves because these were VERY dense bushes. (No access to interior or back leaves easily).

The leaves spread on ground Photo is from the beginning of the problem. The damaged leaves were closest to the soil. Now, the pictures show spots all over the plants – worse on the plants on left half of garden – which are close up in photo.

Answer 1

The dense planting and lack of airflow has likely led to fungal issues.

Though you many be able to control some of the issue, without improvement in growing conditions you may have trouble reversing the issue.
https://www.gardeningknowhow.com/plant-problems/disease/plant-leaf-spots.htm