The relevant section of code should be modified as follows:

<MudDataGrid Class="table" Items="context.Vendors"  >
    <Columns>
        <MudBlazor.PropertyColumn Property="@(vendor => vendor.Name)" />
        <MudBlazor.PropertyColumn Property="@(vendor => vendor.Description)" />
        <MudBlazor.TemplateColumn Title="Action" Context="vendor">
            <CellTemplate>
                <MudLink Href="@($"vendors/edit?id={vendor.Item.Id}")">Edit</MudLink>
            </CellTemplate>
        </MudBlazor.TemplateColumn>
    </Columns>
</MudDataGrid>

My chief errors were not using CellTemplate, and not understanding .Item.*