@stonejames when you mention that turning off hardware acceleration has an impact, that tells us that the issue is with the GPU. I’d make sure that you have all drivers updated and that you revisit your graphics settings.
For example, there was someone with a similar issue and they resolved it by resetting their graphics and doing a clean install of the driver. High GPU load on YT and Twitch
Similar situation at Fan throttling (w11) for no reason
Better way might be to create a new browser profile and make sure not to add any extensions to it. This won’t get rid of your existing profile, but just will create a secondary one to use for troubleshooting.
Other thing to do as well is check everything at brave://flags and putting back to default if you changed anything before.
Other thing you and others may want to check is your settings under brave://settings/system. For example:
** NOTE **
Do keep in mind that any changes made to brave://flags or any custom content filters you add to Shields will persist across profiles on the same device. So if you create new profiles for testing, those are things you also have to consider and change.