I looked for a powershell command to get distribution groups and members in one command but it seems it’s not possible.

So I used an expression to merge them. You can check my following code:

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Get-DistributionGroup | Select Name, @{label="Members";expression={($_ | Get-DistributionGroupMember).Name}}

Output will be like:

You can see all other fields by using:

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Get-DistributionGroup | Select *, @{label="Members";expression={($_ | Get-DistributionGroupMember).Name}}

You can also add other field by using additional expressions.