layer = iface.activeLayer()
features = layer.getFeatures()
feature_list = list(f for f in features)
feat = feature_list[0]
iface.openFeatureForm(layer, feat, True)

from qgis.gui import QgsMapToolIdentifyFeature
from PyQt5.QtGui import QCursor

def onFeatureIdentified(feat):
    iface.openFeatureForm(layer, feat, True)

mapTool = None
canvas = iface.mapCanvas()
layer = iface.activeLayer()
mapTool = QgsMapToolIdentifyFeature(canvas)
mapTool.setLayer(layer)
cursor = QCursor()
cursor.setShape(Qt.WhatsThisCursor)
mapTool.setCursor(cursor)
canvas.setMapTool(mapTool)
mapTool.featureIdentified.connect(onFeatureIdentified)