<ul> and <ol> must only directly contain <li>, <script> or <template> elements
Moderatelist
What it checks
Ensure that lists are structured correctly
How to fix it
Ensure list items are contained within <ul>, <ol>, or <dl> elements
WCAG
Success criteria 1.3.1. See the WCAG 2.2 quick reference.
More detail: Deque University's page on this rule.