I have migrated from J3 to J4.2.8. PHP 8

I have installed the Helix Ultimate template.

I am seeing this error

Warning: Attempt to read property "template" on null in C:\xampp\htdocs\mysite\plugins\system\helixultimate\helixultimate.php on line 217 Default Layout file is not exists! Please goto to template manager and create a new layout first.

This is a very vague error and means nothing to me (or anyone that isn;t the template developer).

Can someone help?