I had the same experience moving from visual studio 2017 to visual studio 2019. I tried disabling every possible IntelliSense related feature and there was always a small but perceptible amount of input latency that drove me crazy.
Eventually I was forced to switch over to jet brains rider and I haven't looked back since, which is a shame because I really enjoyed using the previous versions (2010, 2012, 2015, and 2017).
Eventually I was forced to switch over to jet brains rider and I haven't looked back since, which is a shame because I really enjoyed using the previous versions (2010, 2012, 2015, and 2017).