Xert Claims my FTP (Functional Threshold Power) Sits At 265 Watts. Is It Accurate?

I've always wondered if calculated Functional Threshold Power Values are accurate. Since 2017, however, I have relied on the Xert FTP value. For years, we relied on the "20-Minute" Test. Riders would perform a 20-Minute effort, all out, and then subtract 5% from that value. The new number was considered "Threshold". Later, physiologists looked at 90% of a 3-Minute Maximal Effort. There's the 5-1-5 test.... Step Tests (25w steps every 3 minutes)... Ramp tests (15-20w every minute)... The latest 'Testing' asks for a 20-minute, 5-minute, 1-minute, and 5-second effort.

NO MORE TESTING???.