Human emotions, from a scientific perspective, is still quite a blurry topic. There is no clear distinction between feelings, emotions, affects. Even in scientific context most of the time we are using those terms with their dictionary, or rather 'common-sense' meaning. There is no clear scientific definition (afaik).
In the science of psychology it was poisoned by the "mind-body dualistic" superstitions, even among the famous researchers.
Already Charles Darwin shined some light on evolutionary function of emotions.
Paul Ekman coined his famous theory of basic/prototypical emotions and shown their direct linkage with facial expressions among human species. But already it was shown not to be accurate, if not disproved.
Robert Plutchik build a nice classification model of emotional responses in a psychoevolutionary context. I am not sure how extensively this particular theory was tested and proven.
Lisa Feldman-Barret proposed recently theory of constructed emotions which emphasises their cognitive (and social-adaptive) aspect.
In the field of neuroscience researchers like Mark Solms have shown some underlying mechanisms in a deep brain and cortex that are directly involved in generating 'things' that we usually call emotions or feelings.
What is the current (2021 CE) state-of-the-art theory of emotion/affect/feelings? Who among the top researchers and institutions is trying to solve this problem from a scientific perspective?