Running on an HP Gen 10 Xenon microserver the CPU usage has gone from 0-3% to 25-30% after the upgrade from 20.7.8 to 21.1
From System: Diagnostics: Activity the cause looks to be due to high lighttpd load:
WCPU
100.00% /usr/local/sbin/lighttpd -f /var/etc/lighty-webConfigurator.conf
Update:
I originally posted as the high CPU was seen before and after a firewall reboot.
Having closed the browser (Brave on Linux) for an extended period (> 60m) CPU usage has returned to normal.
This was likely fixed in lighttpd 1.4.59 (included in OpnSense 21.1.1, released 9 Feb 2021)
https://git.lighttpd.net/lighttpd/lighttpd1.4/commit/471ab4dd5bbf752c24fdd11bfcaf163b4769cfce
https://forum.opnsense.org/index.php?topic=21386.0