Plotly custom buttons overflow

This is not the most generalizable solution, but you can pass a separate dictionary of the same buttons (with the y coordinate offset) to the updatemenus parameter of fig.update_layout, where you are defining the buttons.

I had to use trial and error to determine how many buttons fit into a row, and what spacing looks best. Ideally there would be some way to access the size of the button in the same units that are being passed to the parameters x and y.

import plotly.graph_objects as go

import pandas as pd

# load dataset
df = pd.read_csv("https://raw.githubusercontent.com/plotly/datasets/master/volcano.csv")

# create figure
fig = go.Figure()

# Add surface trace
fig.add_trace(go.Surface(z=df.values.tolist(), colorscale="Viridis"))

# Update plot sizing
fig.update_layout(
    width=800,
    height=900,
    autosize=False,
    margin=dict(t=0, b=0, l=0, r=0),
    template="plotly_white",
)

# Update 3D scene options
fig.update_scenes(
    aspectratio=dict(x=1, y=1, z=0.7),
    aspectmode="manual"
)

# Add dropdown
fig.update_layout(
    updatemenus=[
        dict(
            type = "buttons",
            direction = "left",
            buttons=list([
                dict(
                    args=["type", "surface"],
                    label="3D Surface",
                    method="restyle"
                ),
                dict(
                    args=["type", "heatmap"],
                    label="Heatmap",
                    method="restyle"
                )
            ]*4),
            pad={"r": 10, "t": 10},
            showactive=True,
            x=0.11,
            xanchor="left",
            y=1.1,
            yanchor="top"
        ),

        ## offset the y coordinate in these buttons
        dict(
            type = "buttons",
            direction = "left",
            buttons=list([
                dict(
                    args=["type", "surface"],
                    label="3D Surface",
                    method="restyle"
                ),
                dict(
                    args=["type", "heatmap"],
                    label="Heatmap",
                    method="restyle"
                )
            ]*4),
            pad={"r": 10, "t": 10},
            showactive=True,
            x=0.11,
            xanchor="left",
            y=1.15,
            yanchor="top"
        )
    ]
)

# Add annotation
fig.update_layout(
    annotations=[
        dict(text="Trace type:", showarrow=False,
                             x=0, y=1.1, yref="paper", align="left")
    ]
)

fig.show()