Hello: I have seen trees leaf out very late, yet your description suggests otherwise. If there are no buds or very small buds produced for 2020 that did not open or no buds at all the tree gave up last summer. Looking at annual rates of growth the past 5 years would tell you a lot. If they were average for a number of years and then in the last 2-3 shortened up more and more is suggesting a decline in health. The winter of 18-19 was brutal and that could have started the decline. If the tree was very healthy and this happened all at once, I would consult with a qualified Arborist and discuss systemic diseases. This is important especially if you have other oaks. Right now you can check for any live tissue just below the twigs and branches. lightly scrape the twing and if alive the color will be a moist looking dark green color. if it is light green and dry looking, then in decline. if brown and or the branches and twigs snap, there is no life present.
