Is there a standard component for collapsible panel in Qt?

I decided to follow the general approach laid out in the link provided by Joey.

Specifically, I created a widget for each collapsible list. This widget consists of a QPushButton at the top and a QListView at the bottom.

Then, I wired the button clicked signal to a handler to toggle the geometry of the QListView between having height of 0 when it is hidden and its original height when it reappears.

I find that this approach is much simpler compared to customizing the paint event as suggested by Claudio. Furthermore, I can use QAnimationProperty to animate the change in geometry to make the list appear to "slide" in and out of view.

But anyway thanks for the replies!

I created the collapsible panel. Here's the Code:

import os
import sys 
from pathlib import Path
from PySide2.QtWidgets import QPushButton, QVBoxLayout, QApplication ,QListWidget, QListView, QLabel, QWidget, QAbstractItemView, QSplitter 
from PySide2.QtGui import QStandardItemModel, QStandardItem, QIcon, Qt, QDrag
from PySide2 import QtCore

PATH = os.path.join('.','img_src')
print('LayerSelector Loaded with path:' , PATH)

class CustomQStandardItem(QStandardItem):
    def __init__(self, icon, text):
        super().__init__(icon, text)
    
    def dropMimeData(self, data, action, row, column, parent):
        pass
        
class LayersList(QWidget):
    '''
    LayerList class which acts as collapsable list.
    '''
    def __init__(self, name, layers, expand = True):
        super().__init__()
        self.currently_expanded = True
        self.main_layout = QVBoxLayout()
        self.main_layout.setMargin(0)
        self.main_layout.setSpacing(0)
        self.main_layout.setContentsMargins(0, 0, 0, 0)
        self.expand_button = QPushButton(name)
        self.expand_button.setToolTip(f"List of {name} Layers")
        self.expand_button.setIcon(QIcon(os.path.join(PATH,'LayersList_Up.png')))
        self.layer_list = QListView()
        self.layer_list.setDragEnabled(True)
        self.container_model = QStandardItemModel()
        for l in layers:
            qs = CustomQStandardItem(QIcon(os.path.join(PATH,'LayersList_Layer_Icon.png')),l)
            self.container_model.appendRow(qs)
        self.layer_list.setModel(self.container_model)
        self.layer_list.setEditTriggers(QAbstractItemView.NoEditTriggers)
        self.main_layout.addWidget(self.expand_button,0, Qt.AlignTop)
        self.main_layout.addWidget(self.layer_list, 0, Qt.AlignTop)
        self.expand_button.clicked.connect(self.expand)
        self.setLayout(self.main_layout)
        self.resized_size = 16.5 * len(layers)
        self.set_styling()
        if not expand:
            self.expand()
            
    @QtCore.Slot()
    def expand(self):
        if self.currently_expanded:
            self.layer_list.setMaximumHeight(0)
            self.expand_button.setIcon(QIcon(os.path.join(PATH,'LayersList_Down.png')))
            self.currently_expanded = False
        else:
            self.layer_list.setMaximumHeight(self.resized_size)
            self.expand_button.setIcon(QIcon(os.path.join(PATH,'LayersList_Up.png')))
            self.currently_expanded = True
            
    def set_styling(self):
        self.setStyleSheet("background-color:aliceblue ;")
        self.expand_button.setStyleSheet("text-align:left;")
        self.layer_list.setStyleSheet("background-color:aliceblue; border:1px solid;border-style: ridge;")

class LayersSelectorWidget(QWidget):
    '''
    LayerChoiceWidget class provide widget plugin for picking layers.
    '''
    def __init__(self):
        super().__init__()
        names = ['Core Layers',
                 'Convolution Layers',
                 'Pooling Layers',
                 'Recurrent Layers',
                 'Preprocessing Layers',
                 'Attention Layers',
                 'Reshaping Layers',
                 'Locally-Connected Layers'
                 ]
        layers = [
            ['Dense', 'Activation', 'Embedding', 'Masking', 'Lambda'],
            ['Conv1D', 'Conv2D', 'Conv3D', 'SeparableConv1D', 'SeparableConv2D', 'DepthwiseConv2D', 'Conv2DTranspose', 'Conv3Dtranspose'],
            ['MaxPooling1D', 'MaxPooling2D', 'MaxPooling3D', 'AveragePooling1D', 'AveragePooling2D', 'AveragePooling3D', 'GlobalMAxPooling1D', 'GlobalMAxPooling2D', 'GlobalMAxPooling3D', 'GlobalAveragePooling1D', 'GlobalAveragePooling2D', 'GlobalAveragePooling3D'],
            ['LSTM', 'GRU', 'SimpleRNN', 'TimeDistributed', 'BiDirectional', 'ConvLSTM2D'],
            ['TextToVector', 'Normalization'],
            ['Attention', 'AdditiveAttention'],
            ['Reshape', 'Flatten', 'Cropping1D', 'Cropping2D', 'Cropping3D', 'UpSampling1D', 'UpSampling2D', 'UpSampling3D', 'ZeroPadding1D', 'ZeroPadding2D', 'ZeroPadding3D'],
            ['LocallyConnected1D', 'LocallyConnected2D']
        ]
        self.main_layout = QVBoxLayout()
        for i in range(len(names)):
            if i > 3:
                self.main_layout.addWidget(LayersList(names[i], layers[i], False))
            else:
                self.main_layout.addWidget(LayersList(names[i], layers[i]))                
        self.main_layout.setSpacing(0)
        self.main_layout.setAlignment(Qt.AlignTop)        
        self.main_layout.setMargin(0)
        self.main_layout.setSpacing(0)
        self.main_layout.setContentsMargins(0, 0, 0, 0)
        self.setLayout(self.main_layout)
        del(names)
        del(layers)
        self.set_styling()
        
    def set_styling(self):
        self.setStyleSheet("background-color:aliceblue; border:0px solid;border-style: solid;")

Below is the result of above Code :

You can also play with set_styling to change look and feel.