You can hide the dropdown arrow from the Dropdown Menu by adding class e-caret-hide
to Dropdown Menu element using CssClass
property.
@using Syncfusion.Blazor.SplitButtons
<SfDropDownButton CssClass="e-caret-hide" Content="Message">
<DropDownMenuItems>
<DropDownMenuItem Text="Edit"></DropDownMenuItem>
<DropDownMenuItem Text="Delete"></DropDownMenuItem>
<DropDownMenuItem Text="Mark as Read"></DropDownMenuItem>
<DropDownMenuItem Text="Like Message"></DropDownMenuItem>
</DropDownMenuItems>
</SfDropDownButton>
Output be like