I was invited to the AppleSeed beta yesterday and have installed Safari Version 14.0 (15610.1.20.4, 15610) on Catalina (10.15.6) - unfortunately it seems to love CPU usage.
With only Safari open, with no websites and all extensions disabled, it consistently uses 100% of the CPU on my MacBook Pro. As you start to actually use Safari, this usage climbs.
With just two websites open (https://developer.apple.com/download/ and this page https://developer.apple.com/forums/create/question), Activity Monitor reports that Safari is using 1,196% CPU and the fans are going full speed.
Is anyone else using the Safari beta on Catalina experiencing the same?
I've just reported this via Feedback Assistant.