Safari is "using significant energy" even when closed
A couple of weeks back I had concerns about my MacBook heating up above the Touch Bar and such, and noticing that it happened often when using Safari. Tonight, I had closed the Safari app early when I noticed that under the battery icon in the top bar, it still showed Safari "using significant energy" for a few minutes after it had closed. And tested a few minutes later, using only one window open iwht a site that doesn't play videos, and the message was back there. Is there a problem with Safari that could be doing all this? I have no extensions or plugins added, and have added an EtreCheck report (I haven't had time to back the machine up with Time Machine due to being swamped with work on another laptop). Any help would be appreciated, I'm not sure if this is a bug in Safari and if it is wrecking my MacBook.
MacBook Pro 16″, macOS 11.6