import plotly.graph_objects as go

fig = go.Figure()

fig.add_shape(
    type="line",
    xref="x",
    yref="y",
    x0=4,
    y0=0,
    x1=8,
    y1=1,
    line=dict(
        color="LightSeaGreen",
        width=3,
    ),
    legendgroup="group",  # this can be any string, not just "group"
    name="first legend group",
    showlegend=True,
)
fig.add_shape(
    type="line",
    xref="paper",
    yref="paper",
    x0=0,
    y0=0,
    x1=0.5,
    y1=0.5,
    line=dict(
        color="DarkOrange",
        width=3,
    ),
    legendgroup="group",  # this can be any string, not just "group"
    name="first legend group B",
    showlegend=False,
)

fig.show()

import plotly.graph_objects as go

fig = go.Figure()

fig.add_trace(go.Scatter(
    x=[1, 2, 3],
    y=[2, 1, 3],
    legendgroup="group",  # this can be any string, not just "group"
    name="first legend group",
    mode="markers",
    marker=dict(color="Crimson", size=10)
))

fig.add_trace(go.Scatter(
    x=[1, 2, 3],
    y=[2, 2, 2],
    legendgroup="group",
    name="first legend group - average",
    mode="lines",
    line=dict(color="Crimson"),
    showlegend=False,
))

fig.add_trace(go.Scatter(
    x=[1, 2, 3],
    y=[4, 9, 2],
    legendgroup="group2",
    name="second legend group",
    mode="markers",
    marker=dict(color="MediumPurple", size=10)
))

fig.add_trace(go.Scatter(
    x=[1, 2, 3],
    y=[5, 5, 5],
    legendgroup="group2",
    name="second legend group - average",
    mode="lines",
    line=dict(color="MediumPurple"),
    showlegend=False
))

fig.update_layout(title=dict(text="Try Clicking on the Legend Items!"))
fig.show()