The tweet mentions a bypass technique for XSS using the 'XSS without parentheses' trick. The payload crafted a BXSS payload that successfully bypassed a bug bounty target's relatively strict WAF. More details about the WAF vendor are not provided in the tweet. The bypass technique used seems effective and was acknowledged as fun by the user. It would be interesting to analyze further details if available.
For more details, check out the original tweet here: https://twitter.com/_lauritz_/status/1922239072602358034