Thanks @efahl and @acid8000 for your helpful inputs. Indeed, after physically removing the wifi card (Compex wle600vx) the CPU achieves the lower frequency as expected. It seems that the kernel commit to move to a tickless timer doesn't play well with an older CPU paired with an mPCIe wifi card based on the Qualcomm Atheros QCA9882 chipset. It may be an edge case as it may be a combination of these two chips only. Unclear without another card being tested.
I still have the issue with webservers in v24.10.0 not fetching data albeit no issues with serving other devices and routing traffic when connected to the router. All internet connectivity is fine from the router and connected devices but weirdly not when the router is serving a webpage.
EDIT: deleting images to avoid burdening the server.
There seem to be a number of issues with dnsmasq and unbound. My issue is likely related to the resolution of some addresses that aren't resolved. Using unbound, www.gstatic.com isn't resolved at all.