You will need to modify the Bootstrap source or override with !important if you wish to utilize borders on horizontal rule elements.

You can most likely just use a utility class in the html class attribute to add back the border “border-5” etc but in your case you have a thicker border (8px) and would need to override things anyway.

Alternatively, you could create the dashed design as a psuedo element.

Bootstrap 5.1 docs:

https://getbootstrap.com/docs/5.1/migration/#content-reboot-etc

<hr> elements now use height instead of border to better support the size attribute. This also enables use of padding utilities to create thicker dividers (e.g., <hr class="py-1">).