I am using the radslider and have it oriented horizontally but it displays vertically. I attached a screenshot below.
<div class="column is-half">
<small>Weeks ahead to buy</small><br />
<strong><TelerikSlider @bind-Value="@Value"
Min="0"
Max="6"
SmallStep="1"
LargeStep="2"
Width="350px"
Orientation="SliderOrientation.Horizontal">
</TelerikSlider></strong>
</div>
Double check that you are referencing the correct Telerik stylesheet (see more here) and try removing custom CSS from the page/project - there may be some generic rule that affects the slider as well (say, some flexbox setting).